The shape of powder grains has a profound effect on the performance of the powder charge, as it concerns both pressure and velocity. There are multiple powder shapes including flake, ball, and extruded or “stick” (both solid and perforated).
So how does powder grain shape affect pressure and muzzle velocity?
In general, it can be said that powder that burns progressively achieves a desired muzzle velocity at lower maximum pressure than a powder that burns neutrally, not to mention a degressive powder. As grain size increases, the maximum pressure moves towards the muzzle, also increasing muzzle blast. Muzzle velocity and pressure can be adjusted by means of the amount of powder or loading density, i.e. the relationship between the powder mass and the volume available to it. As the loading density increases, maximum pressure grows.
All Vihtavuori reloading powders are of the cylindrical, single-perforated extruded stick type. The differences in burning rate between the powders depend on the size of the grain, the wall thickness of the cylinder, the surface coating and the composition. Cylindrical extruded powders can also have multi-perforated grains. The most common types are the 7- and 19-perforated varieties. A multi-perforated powder grain is naturally of a much larger size than one with a single perforation, and is typically used for large caliber ammunition.
Other types of powder grain shapes include sphere or ball, and flake. The ball grains are typically used in automatic firearms but also in rifles and handguns. The ball grain is less costly to produce, as it is not pressed into shape like cylindrical grains. Flake shaped grains are typically used in shotgun loadings.
Web thickness in gunpowder terminology means the minimum distance that the combustion zones can travel within the powder grain without encountering each other. In spherical powders, this distance is the diameter of the “ball”; in flake powder it is the thickness of the flake; and in multi-perforated extruded powders it is the minimum distance (i.e. wall thickness) between the perforations.
The burning rate of powder composed of grains without any perforations or surface treatment is related to the surface area of the grain available for burning at any given pressure level. The change in the surface area that is burning during combustion is described by a so-called form function. If the surface area increases, the form function does likewise and its behavior is termed progressive. If the form function decreases, its behavior is said to be degressive. If the flame area remains constant throughout the combustion process, we describe it as “neutral” behavior.
The cylindrical, perforated powders are progressive; the burning rate increases as the surface area increases, and the pressure builds up slower, increasing until it reaches its peak and then collapses. Flake and ball grains are degressive; the total powder surface area and pressure are at their peak at ignition, decreasing as the combustion progresses.
Here’a useful article by Sierra Bullets Media Relations Manager Carroll Pilant. This story, which originally appeared in the Sierra Bullets Blog, covers some of the more common ammo problems that afflict hand-loaders. Some of those issues are: excessive OAL, high primers, and improperly-sized cases. Here Mr. Pilant explains how to avoid these common problems that lead to “headaches at the range.
I had some gentlemen at my house last fall getting rifle zeros for an upcoming elk hunt. One was using one of the .300 short mags and every 3rd or 4th round would not chamber. Examination of the case showed a bulge right at the body/shoulder junction. These were new cases he had loaded for this trip. The seating die had been screwed down until it just touched the shoulder and then backed up just slightly. Some of the cases were apparently slightly longer from the base to the datum line and the shoulder was hitting inside the seating die and putting the bulge on the shoulder. I got to thinking about all the gun malfunctions that I see each week at matches and the biggest percentage stem from improper handloading techniques.
One: Check Your Cases with a Chamber Gage
Since I shoot a lot of 3-gun matches, I see a lot of AR problems which result in the shooter banging the butt stock on the ground or nearest solid object while pulling on the charging handle at the same time. I like my rifles too well to treat them that way (I cringe every time I see someone doing that). When I ask them if they ran the ammo through a chamber gage, I usually get the answer, “No, but I need to get one” or “I didn’t have time to do it” or other excuses. The few minutes it takes to check your ammo can mean the difference between a nightmare and a smooth running firearm.
A Chamber Gauge Quickly Reveals Long or Short Cases
Size Your Cases Properly
Another problem is caused sizing the case itself. If you will lube the inside of the neck, the expander ball will come out a lot easier. If you hear a squeak as the expander ball comes out of a case neck, that expander ball is trying to pull the case neck/shoulder up (sometimes several thousandths). That is enough that if you don’t put a bulge on the shoulder when seating the bullet … it can still jam into the chamber like a big cork. If the rifle is set up correctly, the gun will not go into battery and won’t fire but the round is jammed into the chamber where it won’t extract and they are back to banging it on the ground again (with a loaded round stuck in the chamber). A chamber gage would have caught this also.
Oversizing cases also causes problems because the firing pin doesn’t have the length to reach the primer solid enough to ignite it 100% of the time. When you have one that is oversized, you usually have a bunch, since you usually do several cases at a time on that die setting. If the die isn’t readjusted, the problem will continue on the next batch of cases also. They will either not fire at all or you will have a lot of misfires. In a bolt action, a lot of time the extractor will hold the case against the face of the breech enough that it will fire. The case gets driven forward and the thinner part of the brass expands, holding to the chamber wall and the thicker part of the case doesn’t expand as much and stretches back to the bolt face. If it doesn’t separate that time, it will the next time. When it does separate, it leaves the front portion of the case in the chamber and pulls the case head off. Then when it tries to chamber the next round, you have a nasty jam. Quite often range brass is the culprit of this because you never know how many times it has been fired/sized and in what firearm. Back to beating it on the ground again till you figure out that you have to get the forward part of the case out.
Just a quick tip — To extract the partial case, an oversized brush on a cleaning rod [inserted] and then pulled backward will often remove the case. The bristles when pushed forward and then pulled back act like barbs inside the case. If you have a bunch of oversized case that have been fired, I would dispose of them to keep from having future problems. There are a few tricks you can use to salvage them if they haven’t been fired though. Once again, a case gage would have helped.
Two: Double Check Your Primers
Another thing I see fairly often is a high primer, backwards primer, or no primer at all. The high primers are bad because you can have either a slam fire or a misfire from the firing pin seating the primer but using up its energy doing so. So, as a precaution to make sure my rifle ammo will work 100% of the time, I check it in a case gage, then put it in an ammo box with the primer up and when the box is full, I run my finger across all the primers to make sure they are all seated to the correct depth and you can visually check to make sure none are in backwards or missing.
Three: Check Your Overall Cartridge Length
Trying to load the ammo as long as possible can cause problems also. Be sure to leave yourself enough clearance between the tip of the bullet and the front of the magazine where the rounds will feed up 100%. Several times over the years, I have heard of hunters getting their rifle ready for a hunt. When they would go to the range to sight in, they loaded each round single shot without putting any ammo in the magazine. On getting to elk or deer camp, they find out the ammo is to long to fit in the magazine. At least they have a single shot, it could be worse. I have had hunters that their buddies loaded the ammo for them and then met them in hunting camp only to find out the ammo wouldn’t chamber from either the bullet seated to long or the case sized improperly, then they just have a club.
Four: Confirm All Cases Contain Powder
No powder in the case doesn’t seem to happen as much in rifle cartridges as in handgun cartridges. This is probably due to more handgun ammo being loaded on progressive presses and usually in larger quantities. There are probably more rifle cartridges that don’t have powder in them than you realize though. Since the pistol case is so much smaller internal capacity, when you try to fire it without powder, it usually dislodges the bullet just enough to stick in the barrel. On a rifle, you have more internal capacity and usually a better grip on the bullet, since it is smaller diameter and longer bearing surface. Like on a .223, often a case without powder won’t dislodge the bullet out of the case and just gets ejected from the rifle, thinking it was a bad primer or some little quirk.
For rifle cases loaded on a single-stage press, I put them in a reloading block and always dump my powder in a certain order. Then I do a visual inspection and any case that the powder doesn’t look the same level as the rest, I pull it and the one I charged before and the one I charged after it. I inspect the one case to see if there is anything visual inside. Then I recharge all 3 cases. That way if a case had powder hang up and dump in the next case, you have corrected the problem.
On progressive presses, I try to use a powder that fills the case up to about the base of the bullet. That way you can usually see the powder as the shell rotates and if you might have dumped a partial or double charge, you will notice as you start to seat the bullet if not before. On a progressive, if I don’t load a cartridge in one smooth stroke (say a bullet tipped over sideways and I raised the ram slightly to reset it) Some presses actually back the charge back adding more powder if it has already dumped some so you have a full charge plus a partial charge. When I don’t complete the procedure with one stroke, I pull the case that just had powder dumped into it and check the powder charge or just dump the powder back into the measure and run the case through later.
Redding Reloading offers handy Handloader’s Data Sheets in printable PDF format. This FREE 2-page form allows hand-loaders to document their tool settings, bushing size, powder charge, load specs (COAL etc.), and case prep status on Page 1. Then the second page allows you to enter your load testing information, complete with chronograph data, group size, zero range, and wind/temp conditions. The top of page 2 has fields for listing wind and weather conditions. Then below there are six (6) blocks for 5-shot strings, with places to record ES, SD, Average Velocity, and group size. With this single, handy form you can document all the vital information for your particular cartridges and loads. We suggest you print these out, 3-hole-punch ‘em, and then keep them in a three-ring binder.
We’ve seen various reloading log templates, but this Redding form (shown below) is better than most because it combines both reloading data AND range-test data in one place. You can see all key details of the reloading process (tool settings etc.) plus the end results — how the load actually performed over the chronograph and on paper. This form allows the user to capture a large amount of information for later use, while accurately track load development. CLICK HERE to DOWNLOAD.
FREE Ammunition Box Label Template Redding also provides a FREE printable template for your ammo boxes (see photo at top of article). This lets you put all vital load info on your ammo boxes. There are fields for: Date, Cartridge, Powder, Grains, Bullet, Weight, Primer, Case type. Designed for Avery 5260 (or similar) label sheets, this template allows you to print 30 labels at one time. You can purchase the Avery 5260 peel-off printable label sheets at any office supply store.
Tired of spending $15-$25 for a can of spray lube that doesn’t last that long? For about the same price as a single 10 oz. can you can make your own effective spray lube that should last for multiple seasons and lube thousands of cases quickly and easily.
In the YouTube video embedded below, our friend Gavin Gear of UltimateReloader.com shows how to make your own case lube using simple, inexpensive ingredients. As recommended by the 6.5 Guys, this Liquid Lanolin + Isopropyl Alchohol mix works well and is very cost-effective. You can make a pint of this home-brew Lanolin case lube that will lube thousands of cases — many more than a typical commercial aerosol spray can (that’s mostly compressed air).
Gavin describes the exact mixing process on his Ultimate Reloader website. Gavin says this lube mix is a good complement to the Hornady One-Shot (pistol) and Dillon DCL (rifle) lubes he has used for pistol and rifle reloading sessions. CLICK HERE to read more.
This illustration shows headspace measurement for the popular .308 Winchester cartridge, which headspaces on the shoulder. Image copyright 2015 Ultimate Reloader.
In this Brownells Tech Tip Video, Brownells gun tech Steve Ostrem explains what headspace is and why it’s one of the most critical measurements for nearly all firearms. Even if you’re an experienced rifle shooter, it’s worth watching this video to refresh your understanding of headspace measurements, and the correct use of “GO” and “NO-GO” gauges.
Headspace Definition
In firearms, headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum reference) to the face of the bolt. Different cartridges have their datum lines in different positions in relation to the cartridge. For example, 5.56x45mm NATO ammunition headspaces off the shoulder of the cartridge, whereas .303 British headspaces off the forward rim of the cartridge. If the headspace is too short, ammunition that is in specification may not chamber correctly. If headspace is too large, the ammunition may not fit as intended or designed and the cartridge case may rupture, possibly damaging the firearm and injuring the shooter. (Source: Wikipedia)
Problems Caused by Too Much Headspace
Excessive headspace issues can include: light primer strikes, failure to fire, bulged/blown cases, case separations, split shoulders, or unseated primers after firing. Case ruptures caused by excessive headspace can lead to catastrophic failures causing serious injury. That is why headspace is such an important measurement.
Problems Cause by Too Little Headspace
Insufficent (or excessively tight) headspace can prevent the firearm from going into battery, resulting in failure to fire or deformation of the cartridge case. Various feeding and functioning problems can be caused by cases with too little headspace, even if a round can be chambered (with effort).
Headspace Gauges
Headspace is measured with a set of two headspace gauges: a “Go” gauge, and a “No-Go” gauge. Headspace gauges resemble the cartridges for the chambers they are designed to headspace, and are typically made of heat-treated tool steel. Both a “Go” and a “No-Go” gauge are required for a gunsmith to headspace a firearm properly. A third gauge, the “Field” gauge, is used (as the name implies) in the field to indicate the absolute maximum safe headspace. This gauge is used because, over time, the bolt and receiver will wear, the bolt and lugs compress, and the receiver may stretch, all causing the headspace to gradually increase from the “factory specs” measured by the “Go” and “No-Go” gauges. A bolt that closes on “No-Go” but not on “Field” is close to being unsafe to fire, and may malfunction on cartridges that are slightly out of spec. (Source: Wikipedia)
You need to understand Headspace Gauges and how to use them. There are “Go”, “No-Go”, and “Field” gauges. The “Field” is actually the longest. Brownells explains: “The GO gauge corresponds to the SAAMI minimum chamber length, while the FIELD gauge usually matches the maximum chamber depth, or slightly less. NO-GO gauges are an intermediate length between minimum and maximum, that, technically, is a voluntary dimension. A firearm that closes on a NO-GO gauge and does not close on a FIELD gauge may not give good accuracy and may have very short cartridge case life [.]”
When neck-turning cases, it’s a good idea to extend the cut slightly below the neck-shoulder junction. This helps keep neck tension more uniform after repeated firings, by preventing a build-up of brass where the neck meets the shoulder. One of our Forum members, Craig from Ireland, a self-declared “neck-turning novice”, was having some problems turning brass for his 20 Tactical cases. He was correctly attempting to continue the cut slightly past the neck-shoulder junction, but he was concerned that brass was being removed too far down the shoulder.
Craig writes: “Everywhere I have read about neck turning, [it says] you need to cut slightly into the neck/shoulder junction to stop doughnutting. I completely understand this but I cant seem to get my neck-turning tool set-up to just touch the neck/shoulder junction. It either just doesn’t touch [the shoulder] or cuts nearly the whole shoulder and that just looks very messy. No matter how I adjust the mandrel to set how far down the neck it cuts, it either doesn’t touch it or it cuts far too much. I think it may relate to the bevel on the cutter in my neck-turning tool…”
Looking at Craig’s pictures, we’d agree that he didn’t need to cut so far down into the shoulder. There is a simple solution for this situation. Craig is using a neck-turning tool with a rather shallow cutter bevel angle. This 20-degree angle is set up as “universal geometry” that will work with any shoulder angle. Unfortunately, as you work the cutter down the neck, a shallow angled-cutter tip such as this will remove brass fairly far down. You only want to extend the cut about 1/32 of an inch past the neck-shoulder junction. This is enough to eliminate brass build-up at the base of the neck that can cause doughnuts to form.
The answer here is simply to use a cutter tip with a wider angle — 30 to 40 degrees. The cutter for the K&M neck-turning tool (above) has a shorter bevel that better matches a 30° shoulder. There is also a 40° tip available. PMA Tool and 21st Century Shooting also offer carbide cutters with a variety of bevel angles to exactly match your case shoulder angle*. WalkerTexasRanger reports: “I went to a 40-degree cutter head just to address this same issue, and I have been much happier with the results. The 40-degree heads are available from Sinclair Int’l for $15 or so.” Forum Member CBonner concurs: “I had the same problem with my 7WSM… The 40-degree cutter was the answer.” Below is Sinclair’s 40° Cutter for its NT-series neck-turning tools. Item NT3140, this 40° Cutter sells for $14.99. For the same price, Sinclair also sells the conventional 30° Cutter, item NT3100.
Al Nyhus has another clever solution: “The best way I’ve found to get around this problem is to get an extra shell holder and face it off .020-.025 and then run the cases into the sizing die. This will push the shoulder back .020-.025. Then you neck turn down to the ‘new’ neck/shoulder junction and simply stop there. Fireforming the cases by seating the bullets hard into the lands will blow the shoulder forward and the extra neck length you turned by having the shoulder set back will now be blended perfectly into the shoulder. The results are a case that perfectly fits the chamber and zero donuts.”
A good case trimmer is an essential tool for precision hand-loading. To ensure consistent loads, you want your cases to be the exact same length. Today’s Saturday Showcase features five trimming tools, both powered and manually operated, that can trim your sized brass with great precision. In addition, some of these tools will also chamfer case necks inside and out. The powered case trimmers will save you considerable time (and effort) when working will large batches of brass.
Lead photo shows the Henderson Gen 2 trimmer from Panhandle Precision video review.
Henderson Gen 3 Power Trimmer — Ultimate Reloader Review
Gavin Gear of UltimateReloader.com has tested the impressive Henderson Gen 3 (V3) Trimmer. You’ll find a full write-up on Gavin’s website, and you can watch Gavin’s 18.7-minute video review above.
Gavin states: “The Henderson Gen 3 case trimmer is built on an adjustable tri-trim 3-way cutter with different pilots to accommodate different case necks. Three-way cutters trim to length and chamfer the inside and outside all at once. This trimmer has a 1700 RPM spindle and a custom DC motor made in the USA. The Henderson trimmer works much like a milling machine. You do not need much torque because of the way the taper works. The Henderson Gen 3 trimmer delivered outstanding cartridge length consistency after trimming. This trimmer is fast and easy to use and most importantly, returns consistent results.”
CLICK HERE for Henderson Gen 2 Trimmer video review, which shows how to how to set trim length and change cutter heads, using 6.5×47 Lapua, .260 Remington, and .300 Winchester Magnum cases.
Giraud Power Case Trimmer — Full Review by Erik Cortina
In this video, Erik Cortina of CortinaPrecision.com offers some very clever and useful tips that will help you get the most from your Giraud powered case trimmer. The Giraud trimmer is very precise. When set up correctly, it can trim brass with amazing consistency.
In the video, Erik trims 5 pieces of brass in 15 seconds (6:32 mark). He then measures all five with precision calipers (7:00-8:08). All lengths are exact within .0005 (half a thousandth). Erik notes that the Giraud trimmer indexes off the case shoulder. As long as you have fire-formed brass with consistent base-to-shoulder dimensions, you should get very consistent trim lengths.
Lyman Powered Case Trimmer Review
The Lyman Case Trim Xpress is an efficient, precise unit that allows easy adjustment of trim length with a click-adjustable collar. The trimmer comes with a set of cartridge-specific bushings that index off the case shoulder. One nice feature is a variable speed control. For the price, $146.20 on Amazon, this trimmer delivers excellent performance. To see more details, check out F-Class John’s video review of the Lyman Case Trim Xpress which shows set-up and operation.
Frankford Arsenal Universal Case Trimmer (for Power Drills)
This video features a handy tool that attaches to a portable drill. Used with various diameter collets, this can trim most popular sizes of shouldered brass. The universal collet system indexes on case shoulders for precise and consistent trimming (this does NOT work with straight-walled cartridges). The built-in depth micrometer allows for quick and precise micro-adjustments. There is a handy brass shaving ejection port. The system works well, particularly if you can stabilize your power drill in one position. This Frankford Arsenal trimmer, under $65.00 on Amazon, is an affordable alternative to the top-end powered case trimmers. It comes with a handy plastic case that holds the trimmer and collets.
L.E. Wilson Manual Case Trimmer
L.E. Wilson, makers of hand dies, case trimmers and other precision reloading tools, makes a popular and precise stainless steel case trimmer with micrometer adjustment. The above video explains the operation of the Wilson trimmer and shows how to trim cases and use the micrometer case length control positioned opposite the hand crank. We definitely like the micrometer control. This feature allows you to set the cartridge overall trim length with great precision. If you are trimming a variety of different cartridge types, the micrometer cut length control comes in very handy.
If you own a L.E. Wilson case trimmer, you should watch the official Accessories Video from L.E. Wilson. This video shows accessories for the L.E. Wilson trimmer. These include: Power Adapter for trimming (replaces hand crank), Titanium Case Trimmer Cutter (longer life), Inside Case Neck Reamer, Primer Pocket Reamer (removes military crimps), Uniform De-Burring Tool, Neck Chamfer Tool (30° and 45°), and handheld inside/outside deburring tool (and power adapter).
BONUS Video: How Important is Consistent Case Length?
This Primal Rights video explains why it is important to maintain precise case lengths if you want best accuracy and most consistent ES/SD. You’ll want to size your cases BEFORE trimming if your trimmer indexes off the case shoulders.
Shown are funnel with ultra-long drop tube (which helps get more kernels in the cases), RCBS Chargemaster (in wood box), and Hood Press (similar to Harrell’s Combo press).
Loading at the range remains important in the Benchrest for Group discipline. In a Special Report below, past IBS President Jeff Stover explains how loading methods (and hardware) have evolved over the years. The advent of accurate, affordable electronic powder dispensers, such as the RCBS ChargeMaster and Frankford’s new Intellidropper, have changed the game and made it easier to load efficiently at the range. And quality manual powder measures are fast and can be very consistent, with a little practice. Loading at the range permits competitors to tune their load to the conditions, change seating depths, or even choose different bullets to suit the barrel’s preferences on any given day.
Although pre-loading is not uncommon, most 100/200-yard group shooters usually load at the match, often between relays. The goal is to shoot smaller groups by staying “in tune”. In a game where 5-shot groups “in the 1s and Zeros” is the goal, tuning loads for the conditions helps deliver match-winning accuracy. Nearly all competitors in this short-range discipline shoot the 6mm PPC cartridge, or a PPC variant.
Loading at the Range — Then and Now
In benchrest shooting for group, loading at the range has been de rigueur for decades. In the Score discipline, preloading is usually the custom. The main reason is that, in Score competition, only one Aggregate (warm-up match and five record targets) per day is usually shot. That would be less than 50 shots, assuming a few sighter shots. Also, the 30BR, the dominant Benchrest-for-Score cartridge, is very amenable to pre-loading.
By contrast, the Group discipline includes 21 targets (two warm-ups and twenty record targets) over a weekend, usually shot with 6PPC-chambered rifles. Many times, the 6PPC shooters may tweak their loads through the day given changing atmospheric conditions or simply trying to find the correct tune to “dot up”. This term, “Dot up”, means the shots are essentially going through the same hole, or closely so.
Loading at the range was a bit different when benchrest competition was in its infancy. The 1951 book, Modern Accuracy by Bob Wallack, is the best of the early benchrest books. Copies can be found, from time to time, on eBay or Alibris. It is a fascinating survey of benchrest as it existed more than six decades ago. There’s even coverage of a controversial target that was argued over at the time. In it, there is a photo of Wallack using the rear bumper of a car at the bench to clamp his reloading tools. Things have come a long way compared to the range loading set-ups of modern shooters. Here you can see Bob Wallack way back in 1950:
Modern loading bench set-ups shown in this Special Report belong to top shooters Howie Levy, Bob Hamister, and Kent Harshman.
The Tactical Rifle Shooters Facebook Group recently showcased tools used to measure case headspace before and after “bumping” the shoulder. After a case is fired, hand-loaders who full-length size their cases will typically bump the shoulders back anywhere from .001″ to .0035″, depending on the rifle and application. With our 6mmBR and Dasher cases we like about .0015″ bump.
You want the amount of case sizing and bump to be the same for all your brass. To ensure uniformity, it makes sense to measure your cases before and after the FL sizing process. When we have time, we check every case. Other folks will simply check the first 3-4 cases coming out of the FL sizing die to ensure the FL die setting is correct and delivering desired headspace/bump.
Whidden Gunworks Shoulder Bump Gauge
There are a variety of tools that can be used to measure shoulder bump. Our favorite is a special cartridge-specific bushing made by Whidden Gunworks. The Whidden Shoulder Bump Gauge enables you to adjust your sizing die to the desired measurement. The bump gauge is attached to your calipers with a set screw and determines the measurement from the base to the shoulder of the case. The photo below, from Tactical Rifle Shooters, shows the Whidden Bump Gauge for the .375 CheyTac cartridge.
Dave Manson Vertical Comparator with Dial Read-Out
Dave Manson states: “This tool was designed to make life easier for the advanced shooter and re-loader by allowing precise measurement of ammunition, case, and chamber headspace. With this information, the re-loader will be able to fine-tune clearances and fits between his ammunition and chamber, with resultant improvements in accuracy and case life.” The functions of the Manson Dial Cartridge Comparator are:
1. Measure headspace of factory or reloaded ammunition
2. Quantify chamber headspace by measuring headspace of a fired case
3. Ensure minimal shoulder set-back when setting up re-loading dies
4. Compare base-to-ogive length to ensure consistent bullet-to-rifling relationship.
In addition to the Dial Indicator and Stand, the $180.00 Dial Cartridge Comparator is supplied with multiple Datum Blocks of precise length and inside diameter (.3300″/.3750″/.4000″/.4375″). MORE INFO HERE.
Hornady L-N-L Headspace Comparator System
Hornady’s Lock-N-Load Headspace Comparator system is easy-to-use and handy. You can get a kit with Red bushing-holder body and 5 bushings for $43.99 at MidwayUSA. Hornady explains: “The Lock-N-Load® Headspace Comparator… gauge measures variations in brass before and after firing or re-sizing. It allows for headspace comparison between fire-formed brass and re-sized brass.” IMPORTANT: Hornady states: “To determine the proper bushing diameter for your cartridge, simply add the neck diameter and the shoulder diameter and divide that number by two. Use the bushing closest to that number.” Hornady offers seven: .188″, .240″, .330″, .350″, .375″, .400″, and .420″.
One tip — We have found the Hornady gauges may vary a little from unit to unit even with the same nominal size. If you have more than one gauge for the same cartridge, test each on your brass — you may then note a slight difference in your bump measurements. Mark one and use that consistently. There is also an Anvil Base Kit that mounts to the opposite blade on the caliper. This provides a more stable surface for the base of your case.
L.E. Wilson Case Gage Depth Micrometer
If you are looking for precise “bump” measurements without having to mess with calipers and clamp-on gauge blocks, you may want to consider the L.E. Wilson Case Gage Depth Micrometer (currently $140.00). This takes very precise, repeatable measurements, but you need to know your starting point. The manufacturer explains: “Every reloader should know exactly how much your Full Length Sizing Die is pushing back the shoulder. With the NEW Case Gage Depth Micrometer you can do just that! It has never been easier to measure you cases headspace before and after sizing. The Depth Mic allows you to slip the micrometer perfectly over the top of the Gage with your case inserted into the Gage and take a measurement. Micrometer has graduations of .001″. The Case Gage Depth Micrometer is set to a zero of .100″ on the scale at our factory. Because of differences in ‘feel’ and temperature, we include a the Gage Block for you to test Zero and to adjust if necessary.”
Pistol Brass Case DIY Bump Gauge
Last is a “field expedient” set-up if you do not have any of the comparator tools shown above. A sized .45 ACP case (or other suitable pistol case) can be used to measure shoulder bump. The mouth of the pistol case sits on the shoulder of your rifle cartridge brass.
Make sure the .45 ACP case is trimmed square and that it is round. We recommend you first run it through an expander, then size it, trim it and chamfer. Next, take the .45 ACP case and slip it over the neck of a fired, unsized rifle case with the primer removed. Align the two cases between the jaws of your calipers and note the length from rim to rim (See left photo below).
OK, now you have the length for a fired rifle case BEFORE sizing. Next, take a full-length sized rifle case (without primer) and do the same thing, placing the .45 ACP case over the neck of the FL-sized case (Right Photo). The difference between the two numbers is the amount of “bump” or set-back you are applying to the shoulder. Here the difference is .0015″. The amount of bump you need varies with your chamber and your load, but .0015-.002″ is a good initial setting.
Today’s Sunday GunDay article features modern magnum cartridge types favored by F-Open competitors. These cartridges will soon be in the hands of top F-Open shooters. The 2025 F-Class National Championships commence next week at the Winnequah Gun Club in Lodi, Wisconsin. The Mid-Range Championships run August 2-5, 2025, while the Long Range F-Class Championships start on the 6th and run through August 9, 2025. At the Nationals top F-Open and F-TR shooters are aiming their rifles at 600-yard targets. VIEW 2025 F-Class Nationals Match Program HERE.
2025 NRA F-CLASS NATIONAL CHAMPIONSHIPS
NRA F-CLASS MID-RANGE NATIONAL CHAMPIONSHIP AUGUST 2-5, 2025
NRA F-CLASS LONG RANGE NATIONAL CHAMPIONSHIP AUGUST 6-9, 2025
Event hosted by Winnequah Gun Club and sponsored by Brux Barrels, Criterion Barrels, Krieger Barrels, and Silver Mountain Target.
There will be two divisions at The F-Class National Championships: F-Open and F-TR. In F-Open the rifles can shoot any cartridge type (up to .35 caliber) and have a 22-lb (10kg) weight limit. A front rest is allowed, and most shooters favor a rest with a joystick control.
In F-TR, two cartridge types are allowed: .223 Remington (5.56×45) or .308 Winchester (7.62×51 NATO), with no restrictions on bullet weight. F-TR rifles are fired off a bipod attached to the rifle’s fore-end. The F-TR weight limit is 8.25 kilograms, or about 18 pounds. This includes the weight of the rifle, scope, and bipod. A sandbag can be used under the rear of the stock. Because of the lower weight limit, which includes the bipod, F-TR stocks tend to be much slimmer and lighter than F-Open stocks which have wide fore-arms to work with the front rests.
F-Open Cartridge Options — Modern Magnum Options
For Today’s Sunday Gunday Story we feature an article about F-Open chamberings by respected rifle builder and past F-Open National Champion Emil Kovan. In this article, Emil reviews some of the new magnum cartridge options that are being employed by F-Open competitors. Many shooters are still using the .284 Winchester (or variants), but an increasing number are shooting 7mm and .30-caliber cartridges based on magnum cartridge types. The 7mm is probably still the favored caliber for F-Open because 7mm bullets offer great ballistics with less recoil than heavier .30-caliber projectiles.
Cartridges for F-Class Part II — Rise of the Magnums
A few seasons back, I wrote an article on cartridge choices for F-Class shooters. CLICK HERE to READ ARTICLE. Since the first article I wrote, F-Class has continued to grow, and push the limits of precision and accuracy. While the .284 Win and its variants are still the most common F-Open cartridges, more and more top F-Open shooters are using magnum cartridge types to win competitions and set new records. In this article, I will list some of the advantages and disadvantages of the most commonly used magnums, and will cover the strengths and weaknesses of each one of them.
Performance factors we will consider for magnum F-Open cartridges include:
1. Equal or better accuracy than standard chambers
2. Better ballistic performance
3. Enhanced case life
4. Barrel life
Accuracy Potential of Magnum Cartridges for F-0pen Competition
John Meyrs has won four National Mid-Range Championships using the .300 WSM. Tim Vought used the same cartridge to win two Mid-Range Nationals and used a 7-6.5 PRC to win the long range Nationals. Standard .437″ case head (.308 Win head size) cartridges still have more Nationals wins overall, but the magnums are quickly catching up, and my prediction is that magnums will dominate soon.
The accuracy and precision potential of magnums used in F-Class (.300 WSM, 7-270 WSM, 7mm RSAUM or “7 SAUM”, 7-6.5 PRC) is better than non-magnum cartridges because their shapes are closer to the ideal “fat/short” body associated with wider nodes and extreme precision. For example a .300 WSM is proportionally much closer to the 6 PPC, 6 Dasher, and 6 BRA than is the .284 Winchester.
Stunning F-Open rifle with SEB Mini front rest with Blake Machine accessories.
The first thing that comes to mind when magnums are discussed is power and speed. In my humble opinion most shooters are missing out on accuracy because they push their magnums right past the most stable and accurate nodes. Recently I met my good friend from the Army Marksmanship Unit, SFC Brandon Green, at a shooting competition. We discussed the latest and greatest in long-range shooting. I knew that the USAMU had switched from 6.5-284 Norma to 7mm RSAUM several years back, but didn’t know what load they are currently using. Brandon told me that the load featured Berger 180gr hybrids in Nosler cases at 2820 fps. We all know that the 7 SAUM is capable of much higher speeds, “but at around 2820 fps the load/rifle combo will hammer the X-Ring anywhere under any conditions” SFC Green said.
F-Open rifles on the firing line at the Ben Avery Shooting Facility in Phoenix, Arizona.
Most shooters jump right into magnum territory velocities when testing, missing out on better precision at standard chamber speeds. For example, my 30 KMR can easily reach 2880 fps with 230gr Hybrids, and it actually shoots pretty good. But the same rifle at around 2770 fps will absolutely hammer the X-Ring in any condition anywhere. When it’s all said and done, F-Class is a long-range shooting competition at a known distance which requires extreme precision and accuracy. It is not a speed race.
IMPORTANT — Case-Head Dimensions Do Make a Difference
Magnums, when shot within reasonable velocities, on average will give better case life due to the bigger case + lower pressure and “more meat” in the case-head area. For example a 7 SAUM case will outlast a .284 Win case when both are loaded to around 2900 fps.
Disadvantages of Magnum F-Open Cartridges
Perhaps the biggest disadvantage linked to magnums is recoil. Some people complain about developing the “gun shy” syndrome after shooting a magnum for a while. Muzzle blast and recoil are significantly more pronounced in magnums, but that can be easily managed with a properly-built rifle equipped with appropriate recoil mitigation hardware such as RAD and the various butt plates.
F-Open rifle equipped with recoil reduction buttpad system.
Barrel Life — “Barrels are Expendable Components”
It is true that certain magnums can torch a barrel in just a few hundred rounds. But the same is true when improving a 6BR to 6 Dasher for example — barrel life might be reduced significantly. More powder = more heat = diminished accuracy after a certain round count. In my experience, a F-Open magnum’s barrel life is very close to high-performance standard cartridges such as the .284 Shehane or .284 KMR. I “retire” my barrels around 1200 rounds regardless of the cartridge being a magnum or not. After that many rounds most barrels will still shoot OK but will copper up, and you will start seeing those unexplained vertical 9s. The bottom line is this, barrels are expendable components very much like brass. You can’t get the performance of .300 WSM and the barrel life of the .308 Win at the same time. If you want to race in NASCAR, fuel mileage should not be the top priority!
Top Magnum Cartridge Types Used in F-Class Open Division
.300 Winchester Short Magnum
The .300 WSM (Winchester Short Magnum) tops the popularity chart in F-Class Open division. It has been used to win numerous National championships and has set many National records. The .300 WSM’s short/fat case shape, with minimal body taper and 35-degree shoulder, contribute greatly to its outstanding performance at long range. Components are readily available as well. Best brass remains to be Norma, although ADG is just as good and some would even say better, but it is more expensive and harder to get at this time.
The .300 WSM has been described as a “super-sized Dasher”.
For the .30-cal magnums, in my opinion, the best bullets by far are made by Berger. If your rifle does not shoot 215gr, 230gr hybrids, or 210gr VLDs well, you likely have a rifle problem, NOT a bullet issue. My “go to” bullet is the Berger 230gr Hybrid. The 215-grainer is a close second, followed by Berger’s accurate but ballistically inferior 210gr VLD, which I use in calm and steady conditions.
Top powders for the .300 WSM are Hodgdon H4831SC and H4350. I know there are many more powders suitable for the .300 WSM cartridge, but none I have used can match Hodgdon’s consistency when shot in different geographical locations and weather conditions.
7mm Remington Short Action Ultra Magnum
The 7mm RSAUM (aka 7 SAUM) used to be the darling of F-Open. Its case capacity and shape are about perfect for launching 180gr pills with great ballistics and precision. Its popularity faded a little, due to the lack of good brass, and the rise of the improved versions of the .284 Win which can almost match the RSAUM performance. Norma still makes 7 RSAUM brass which is pretty good but little on the soft side and hard to find. ADG is arguably producing the best RSAUM brass right now. It is very uniform, reasonably priced, and seems to hold up very well even when pushed hard. The best bullets are again made by Berger, and those are the 180gr hybrid, 184gr hybrid, and 180gr VLD. Best powders are H4831sc, H4350, and Alliant Reloder 16 and Reloder 23.
7-270 WSM, 7-300 WSM, and 7 WSM
The first two are pretty much identical, the only difference being that the 7-270 WSM is necked up .270 WSM while the 7-300 WSM is a .300 WSM necked down to 7mm. I personally prefer the first one since necking-up is easier than necking-down (with fewer doughnut issues).
The WSM case-based 7mms will give you great velocity flexibility as well as superb precision when tuned well. In the 2013 world championship in Raton NM, I was scoring for a gentleman from Canada who was shooting 7-270 WSM. The wind was blowing pretty hard that day. On one of his shots, just before he pulled the trigger the wind gusted. I remember thinking that’s going to be an 8 for sure. The target came up a line 10! I asked him after the match what he was shooting, and he replied 180s at 3100fps. Although capable of such speeds, I think that potentially better and more consistent accuracy can be achieved at much slower speeds. The best powders and bullets are again Hodgdon and Berger respectively. Best cases are made by Norma and ADG, with Winchester being a third option.
7-6.5 PRC — Popular Wildcat
Last but not least on our chart is the 7-6.5 PRC. This particular cartridge is actually a wildcat. It is a 6.5 PRC necked up to 7mm. It is pretty much identical to the 7 RSAUM with the only differences being a shorter neck and .01″-narrower body. Currently the 7-6.5 PRC is the most requested cartridge that I offer when building new rifles. It seems to fill the gap between the .284 Win and the larger magnums very nicely. It is capable of reaching 3000fps but most shooters are getting their best results around 2920-2950 fps. The biggest advantage of this wildcat is brass. Lapua makes super high-quality, readily-available 6.5 PRC brass. Best powders are H4831sc, H4350, Reloder 16, and Vihtavuori VV 555. The best bullet in my opinion is the 180gr Berger. I am yet to hear about a better-performing bullet in this chamber.
Conclusion In conclusion, magnums are not perfect but their performance advantages should be very seriously considered when building a rifle for long-range F-Class. In part three, I will list the most common wildcat magnums, and present the KMR magnums which will make you (if you haven’t already) buy a magnum action and get a magnum build for sure!
– 2014 F-Class Open National Champion
– 2015 F-Class Open National Championship, Silver Medal
– F-Class Open National Championship Teams, 2015, 2014, 2013, Shooting Team Member
– Over 15 wins in Regional and State Championships in Palma, F-TR, F-Open
– 2013 U.S. National Team Member
– 2023 F-Open Gold Medal Team USA Member, 2023 World Championship in South Africa
Oversizing cases also causes problems because the firing pin doesn’t have the length to reach the primer solid enough to ignite it 100% of the time. When you have one that is oversized, you usually have a bunch, since you usually do several cases at a time on that die setting. If the die isn’t readjusted, the problem will continue on the next batch of cases also. They will either not fire at all or you will have a lot of misfires. In a bolt action, a lot of time the extractor will hold the case against the face of the breech enough that it will fire. The case gets driven forward and the thinner part of the brass expands, holding to the chamber wall and the thicker part of the case doesn’t expand as much and stretches back to the bolt face. If it doesn’t separate that time, it will the next time. When it does separate, it leaves the front portion of the case in the chamber and pulls the case head off. Then when it tries to chamber the next round, you have a nasty jam. Quite often range brass is the culprit of this because you never know how many times it has been fired/sized and in what firearm. Back to beating it on the ground again till you figure out that you have to get the forward part of the case out.
Redding also provides a FREE 
Headspace Gauges
When neck-turning cases, it’s a good idea to extend the cut slightly below the neck-shoulder junction. This helps keep neck tension more uniform after repeated firings, by preventing a build-up of brass where the neck meets the shoulder. One of our Forum members, Craig from Ireland, a self-declared “neck-turning novice”, was having some problems turning brass for his 20 Tactical cases. He was correctly attempting to continue the cut slightly past the neck-shoulder junction, but he was concerned that brass was being removed too far down the shoulder.
There will be two divisions at The F-Class National Championships: F-Open and F-TR. In F-Open the rifles can shoot any cartridge type (up to .35 caliber) and have a 22-lb (10kg) weight limit. A front rest is allowed, and most shooters favor a rest with a joystick control.
In conclusion, magnums are not perfect but their performance advantages should be very seriously considered when building a rifle for long-range F-Class. In part three, I will list the most common wildcat magnums, and present the KMR magnums which will make you (if you haven’t already) buy a magnum action and get a magnum build for sure!
