November 22nd, 2014
Lapua brass is so good that you’ll be tempted to just load and shoot, if you have a “no-turn” chamber. However, some minimal case prep will ensure more uniform neck tension. Keeping your neck tension very uniform allows more consistent bullet seating. That, in turn, usually yields better accuracy, and lower Extreme Spread and Standard Deviation (ES/SD). Lapua brass, particularly 6BR, 6.5×47, .243 Win and .308 Win comes from the factory with tighter-than-optimal necks. Before you seat bullets, at a minimum, you should inside chamfer the case mouths, after running an expander mandrel down the necks. The expander mandrels from both Sinclair Int’l and K&M will both leave the necks with enough neck tension (more than .001″) so you can then seat bullets without another operation. Put a bit of lube on the mandrel before running it down the necks — but remove any lube that gets inside the necks before seating bullets.
Both Sinclair and K&M Tools make a die body specifically to hold expander mandrels. The Sinclair version, is shown above. This $24.99 unit fits caliber-specific expander mandrels ($9.95) which measure approximately .001″ less than bullet diameter for each caliber. This is an updated “Gen II” design that completely captures the mandrel within the die so the mandrel cannot pull out. It also has an O-ring in the die cap that allows the mandrel to self-center within the case neck. Sinclair now offers three sizes of die bodies for expander mandrels: .17 -.310 Caliber (#849-011-715WS); .357 – .50 caliber (#749-008-843WS), and a special .50 Cal die body for large-diameter 50 BMG presses (#749-009-163WS, $49.99). All Generation II dies are machined from stainless steel and the standard diameter 7/8-14 dies include the Sinclair Stainless Steel Split Lock Ring.
Once you run the Sinclair expander mandrel down the necks of Lapua brass, after you account for brass spring-back, you’ll have about .002″ neck tension. This will make the process of seating bullets go much more smoothly, and you will also iron out any dents in the case mouths. Once the case mouths are all expanded, and uniformly round, then do your inside neck chamfering/deburring. The same expander mandrels can be used to “neck-up” smaller diameter brass, or prepare brass for neck-turning.
Forum member Mike Crawford adds: “These expanders can also reduce runout from offset seating. Prior to bullet seating, expand the sized necks to force thickness variance outward. With the Sinclair system, the necks will springback fine, and will not be pulled out of center. This leaves plenty of tension, and bullets seated more centered. I do this, even with turned necks, to get improved seating.”
Mandrels vs. Expander Balls on Decapping Rods
If you haven’t acquired an appropriate expander mandrel for your brass, but you DO have a full-length sizing die with an expander ball, this will also function to “iron out” the necks and reduce tension. However, using a die with an expander ball will work the necks more — since you first size them down, then the ball expands them up again. Typically (but not always), run-out is worse when using an expander ball vs. an expander mandrel.
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November 19th, 2014
Here’s a shocking video showing a massive Kaboom (KB) that literally destroyed an M1 Garand in the hands of a lady shooter. One second she has a classic .30-06 battle rifle in her arms, and the next second she has nothing but a pile of parts. She is fortunate to have survived this incident without apparent serious injury. She may have had a squib (undercharged round) in her prior shot at the 00:12 time-mark. At 00:15 it seems she may have experienced “click no bang” (we can’t tell for sure). The detonation occurs at time-mark 00:25, and is then replayed in slow-motion.
If this Kaboom wasn’t caused by a squib, there might have been a catastrophic failure of the cartridge that failed to fire at 00:15. The shooter herself, posting as ArizonaGirl24 on YouTube, thinks the gun may have fired out of battery. What do you think?
Text accompanying the posting of this video on LiveLeak, states: “A woman, her shooting partner, and their cameraperson are lucky to be alive. Her M1 Garand detonated after she failed to check the barrel for an obstruction due to an apparent squib round….
[After the shot at 00:12] she is obviously aware that something is amiss and seems to check the chamber, but does not unload the rifle to check for the presence of a barrel obstruction.
She raises the rifle and fires it again, causing a catastrophic weapon failure. Parts of the weapon fly in all directions. The video then terminates.”
What happened to the shooter? She reported: “I was very lucky with the outcome. I have lots of splinters and bruising, but nothing broken. My left hand took the brunt of the blow to my wrist and palm of my hand. Still pretty painful, but I will be fine.”
Video tip from Mark LaFevers. We welcome reader submissions.
LESSON ONE: If you experience any kind of malfunction, or what appears to be a light-recoiling (or soft-sounding) shot, you should STOP shooting immediately. Clear the firearm and check for barrel obstructions.
LESSON TWO: Always wear ear and eye protection when shooting any firearm, even rimfires.
LESSON THREE: With a semi-auto gun, ensure the bolt is completely in battery after every shot.
LESSON FOUR: When hand-loading check EVERY round for powder charges prior to seating bullets, and weigh your loaded rounds before boxing them. Also check for high primers on EVERY round. If using a progressive press, use a Lock-Out Die that will alert you to any under-loaded cartridge. Be wary of commercial reloads.
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November 16th, 2014
Most of us assume that if we weigh our powder carefully (down to the tenth of a grain or less) we can achieve a uniform powder fill from case to case in our handloads. Weighing does ensure that the weight of the propellant in each case is the same, but is the column of powder the same by volume each time? “Not necessarily” is the answer. An interesting experiment by our friend Boyd Allen demonstrates that the manner in which you place kernels in the case can make a significant difference in the height of the powder column within the brass case.
Using a Gempro 250 scale, Boyd measured exactly 30.6 grains of Vihtavuori N-133 powder. He then inserted this powder in the same cartridge case multiple times. (The case has a fired primer in place.) But here is the key — Boyd used various filling techniques. He did a slow fill, and a fast fill, and he also experimented with tapping and drop tubes. What Boyd discovered was that you can start with the exact same weight of powder (in fact the very same set of kernels), yet end up with vary different fill heights, depending on how you drop the kernels into the case. Look at the photos. Despite variations in lighting, the photos show the same 30.6 grains of powder, placed in the same cartridge, with four different methods.
Boyd Explains the Procedure Used for his Experiment.
EDITOR’s NOTE: So there is no misunderstanding, Boyd started with a weighed 30.6 grain charge. This identical charge was used for ALL four fills. After a fill the powder was dumped from the case into a pan which was then used for the next fill technique to be tried. So, the powder weight was constant. Indeed the exact same kernels (of constant weight and number) were used for each fill.
Boyd writes: “I used the same powder for all fills, 30.6 gr. on a GemPro 250 checked more than once. All fills employed the same RCBS green transparent plastic funnel. The fast drop with the funnel only overflowed when it was removed from the case neck, and 15 granules of powder fell on the white paper that the case was sitting on. The fast-funnel-only drop with tapping, was done with the funnel in place and the case and funnel in one hand, while tapping the case body with the index finger hard, many times (about 20 fast double taps). My idea here was to “max out” the potential of this tapping technique.
The slow drop with the funnel and 10″-long .22 cal. Harrell’s Precision drop tube, was done by holding the scale pan over the funnel and tapping the spout of the pan repeatedly on the inside of the funnel about 1/3 down from the top, with the scale pan tilted just enough so that the powder will just flow. Many taps were involved, again, to max out the technique.
Again, to be clear, after each case filling, the powder was poured from the case back into the scale pan carefully. You may notice the similarity between the fast drop with the drop tube, and the funnel only with tapping. Although I did not photograph it, fast tube drop and tapping (combined) improved on tapping alone, but only to about half as far down the neck as the slow with drop tube. Due to the endless possible permutations, I picked four and left it at that.
I believe that I can make the rough judgment that the scale pan funnel and drop tube technique, which involved a longer drop period, and probably less velocity at the top of the tube, left more room in the top of the case neck than the slow drop from the measure with the same drop tube. You have both pictures, so you can make the comparison.” — Boyd
Does Powder Column Height Variance Make a Difference?
Boyd’s experiment proves pretty conclusively that the method of dropping a given weight of powder can affect the height of the powder column in the case and the degree of powder compression (when a bullet is seated). He showed this to be true even when the exact same set of kernels (of constant weight) was used in repetitive loadings. This raises some interesting questions:
1. Will subsequent cartridge transport and handling cause the powder to settle so the variances in powder column height are diminished?
2. If significant inconsistencies in powder column height remain at time of firing, will the difference in fill level hurt accuracy, or result in a higher extreme spread in velocity?
3. Is there any advantage (beyond increased effective case capacity) for a tight (low level) fill vs. a loose (high level) fill?
We don’t know the answer to these follow up questions. This Editor guesses that, if we tested low-fill-height rounds vs. high-fill-height rounds (all with same true fill quantity by weight), we might see meaningful differences in average velocity. I would also guess that if you fired 10 rounds that exhibited quite a difference in powder column heights, you might see a higher ES/SD than if you shot 10 rounds loaded with a very consistent powder column height (either high or low). But further testing is needed to determine if these predictions are true.
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November 14th, 2014
Gear Review by German Salazar
This article originally appeared in German Salazar’s Rifleman’s Journal website.
Many of you have doubtlessly read Bryan Litz’s articles in our Daily Bulletin and on his Applied Ballistics website about various current long-range bullets. Bryan’s work carries a great deal of weight in the world of ballistics, so his comments (and mathematical proofs) regarding the benefits of bullet pointing certainly caught my attention. Bullet pointing, like meplat trimming, is an effort to reduce the ballistic inconsistency created by the somewhat jagged tip of the jacket where the bullet forming dies bring it to a point in the manufacturing process. Of course, we could eliminate this problem altogether by shooting closed-tip, open-base bullets like the Lapua D46, but that merely shifts the jacket problem to the other end of the bullet.
In any event, hollow point bullets rule the accuracy world today, so John Whidden, multi-time National Long Range Champion at Camp Perry and a talented gunsmith and designer to boot, came up with a very handy tool to let us make those hollow points pointier. Let’s have a look at John’s tool and see how it works.
The Whidden Bullet Pointing Die System uses a Forster bullet seating die body as its basic structure and that’s a good choice given the quality machining Forster does on these. The real heart of the tool comes in two parts: the caliber sleeve and the pointing die that fits inside the sleeve. In fact, to point up different caliber bullets, you only need to change the caliber sleeve, everything else remains the same. The last item is the bullet base that slips into a standard .308 shellholder and supports the bullet as it goes into the die body.
It took me less than five minutes to get everything set up, including changing the caliber sleeve from 6mm to .30 caliber. John’s instruction sheets are well illustrated and clearly written; you should have no problem getting up and running.
Pointing the bullets is as easy as sizing a piece of brass. You can see in the top photo the difference between a few pointed bullets and a few un-pointed ones. The innermost pointed bullet in the picture was my first attempt and I adjusted the die a little after that, you can see that the others are closed a little more. John even includes a couple of sample bullets so that you can see one done right and one done wrong. That is a nice addition that can help you achieve the desired results.
I think Bryan’s work supports the validity of this concept and John’s tool puts it into practice in a simple-to-use manner that makes it just about impossible to do any damage to the bullet. I have shot pointed bullets in various calibers at many matches now. Pointing is not a “miracle cure”, but I believe that pointing bullet tips can produce long-range accuracy gains, through reduced vertical dispersion, for many popular types of match bullets. The Whidden Bullet Pointing Die System retails for $220.00 (with one insert). Additional die inserts are $42.00 each. Extra caliber sleeves are also $42.00. You can purchase directly from Whidden Gunworks, or from Sinclair International.
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November 1st, 2014
German Salazar has written a very thorough guide to measuring nearly all the critical dimensions of cartridge brass. In his Measuring the Case article, on his Rifleman’s Journal website, German reviews the tools and techniques required to measure everything from case overall length to case neck concentricity. Step-by-step, German shows how to measure: Case Length, Case Body length (below neck), Neck Diameter, Headspace, Base Diameter, Neck Thickness, and Case Neck Concentricity.
If you are an “advanced reloader” or want to be, you should read German’s article. Not only does German explain the most common measuring procedures, he highlights some alternative methods you might not have tried yet. The article also links to related discussions of more complex measurement tasts, such as determining case body wall thickness variation.
Even if you’re not a competitive shooter, measuring your brass can provide important safety benefits. As German explains in the conclusion of his article: “There are obviously a lot of measurements that can be taken on the cartridge case and in some cases, more than one way to take them. However, the first two that any new reloader must learn are case length and neck clearance, these two are safety concerns and if overlooked can results in serious damage to the rifle and injury to you.”
German’s article first appeared in RiflemansJournal.com in 2010.
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October 30th, 2014
Can sustained rapid-fire shooting with no cool-down period wear out a quality barrel more quickly? The answer is “Yes” according to Forum member LCazador, who recently did an interesting comparison test with two .243 Win barrels. He started off with two, identical, match-grade HV taper stainless barrels. Both were NEW at the start of testing, and LCazador shot the same load through each: 95gr match bullets with 38 grains of Hodgdon Varget. After giving both barrels the same, gentle 20-round break-in, 300 rounds were then fired through each barrel — in very different ways. Barrel condition and wear were monitored with a borescope.
Barrel One — Slow Fire, Cool Down Periods, Cleaning Every 50 Rounds
At the end of the 300-round test, Barrel One looked brand new. There was none of the severe fire cracking found in Barrel Two. This barrel was shot no more than 10 times without a cool down and firing was done at a much slower pace. Cleaning for this barrel was done every 50 shots.
Barrel Two — Fast Firing, No Waiting, Cleaning Every 100 Rounds
The second barrel, which received hard use and minimal cleaning, was severely damaged with severe fire cracking at the leade and throat. As a result, the barrel had to be re-chambered. This barrel was shot 100 rounds at time without cleaning and was shot up to 20 times in succession without a cool down.
Don’t let your barrel get too hot, and keep it clean. One afternoon can ruin a barrel!
Monitoring Barrel Wear with Borescope
Some folks worry too much about what their borescopes reveal — many barrels do not have to be “squeaky clean” to perform well. In fact some barrels run better after ten or more fouling shots. However, a borescope can be very helpful when your barrel starts losing accuracy for no apparent reason. Forum member FdShuster writes:
“A borescope is a positive way of backing up your suspicions when the rifle starts to throw an occasional (soon followed by more frequent) wild shot. Using the scope is also an excellent way to determine that the cause is barrel wear and not simply a need for a concentrated cleaning session to remove built up copper and more importantly, carbon fouling.
I’ve had a few barrels that gave every indication of being shot out. But I ‘scoped them out and found the cause to be nothing more than requiring a good cleaning. They then returned to their usual performance. There’s no guessing involved when you are able to get ‘up close and personal’ using the scope. The borescope also provides an excellent view of the all-important condition of the crown. My borescope is one of the most valuable investments I’ve ever made.”
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October 29th, 2014
Chances are that many of you have packed away your ammo and shooting supplies for the winter. Maybe you put your brass in a storage bin that might also contain solvents, old rags, or used bore swabs. Well, if you use any ammonia-based solvents, we suggest you separate the brass and ammo and keep it away from potential ammonia vapors. This is because long-term exposure to ammonia fumes can cause cracks to form in your brass. This can lead to case ruptures and possible injury.
This case-cracking phenomenon has been called Season Cracking, a form of stress-corrosion cracking of brass cartridge cases. Season cracking is characterized by deep brittle cracks which penetrate into affected components. If the cracks reach a critical size, the component can suddenly fracture, sometimes with disastrous results. If the concentration of ammonia is very high, then corrosion is much more severe, and damage over all exposed surfaces occurs. The brass cracking is caused by a reaction between ammonia and copper that forms the cuprammonium ion, Cu(NH3)4, a chemical complex which is water-soluble. The problem of cracking can also occur in copper and copper alloys such as bronze.
Season Cracking was originally observed by the British forces in India a century ago. During the monsoon season, military activity was reduced, and ammunition was stored in stables until the dry weather returned. Many brass cartridges were subsequently found to be cracked, especially where the case was crimped to the bullet. In 1921, in the Journal of the Institute of Metals, the phenomenon was explained by Moor, Beckinsale, and Mallinson. Apparently ammonia from horse urine, combined with the residual stress in the cold-drawn metal of the cartridges, was responsible for the cracking.
Don’t store ammunition (or brass) for long periods in a box or container holding ammoniated solvents:
The Australia Department of Defense (AUSDOD) has also explored the problem of brass cracking caused, at least in part, by exposure to ammonia. A study was done to see whether the amount of cracking (from ammonia exposure) varied according to the duration and temperature of the annealing process used on the brass. CLICK HERE to read AUSDOD Research Report.
Story idea from Boyd Allen. We welcome reader submissions.
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October 23rd, 2014
Sooner or later you’ll want to clean your rifle brass, even if you aren’t fussy about appearance. You can tumble your cases in a vibratory tumbler with dry media, but that can leave cases with a fine layer of dust, or worse yet, clogged flash holes. As an alternative to tumbling, many shooters are experimenting with ultrasonic case cleaning. Here are three tips to achieve the best results when using ultra-sound to clean your brass:
Try a Commercial Ultrasonic Cleaning Solution
As a companion product to its new ultrasonic cleaning tank, Hornady is selling a citric-acid based One Shot™ Sonic Clean™ Solution, that is claimed to speed up cleaning times, and not leave your brass an odd pinkish color like some “home-brew” solutions. We’ve heard good reports about the One-Shot Solution (cartridge case formula) as well as Citranox®. Both products are economical to use since you dilute them heavily with water. For example, Hornady recommends you mix forty (40) parts water to one part of One Shot Sonic Clean.
Forum member Dave B is a chemist/physicist with decades of experience working with the ultrasound process. Dave tried a variety of solutions and he favors a mix of water and Citranox®. Dave notes: “So far I’ve been very impressed with the Citranox. Once- or twice-fired brass clean up very quickly. The worst cases I tried were 6 Dashers that had been fired ten times with Varget and never cleaned. The worst fouling was in the bottom of the case around the flash hole. They took longer and I used a more concentrated cleaning solution but they did come out clean. The price is reasonable. I paid $35 a gallon and for once- or twice-fired cases I dilute the cleaner 100 to 1. There is much less chemical reaction with the brass than there is with vinegar. No weird colors, just shiny bright. I even used it with hot water, which speeds up the cleaning process. The cleaner is mostly detergents with a little citric acid. Even at a 1:75 ratio my $35 worth of cleaner will make 75 gallons of solution.” The price has gone up a bit since Dave acquired his Citranox, but Amazon.com sells Citranox for $45.50 per gallon.
Another good ultrasonic solution is L&R non-ammoniated Safety Cleaning Solution, sold by Brownells, item #515-000-004. Brownell’s L&R solution is non-toxic and biodegradeable. The strong surfactant in L&R solution helps penetrate the grit so the ultrasonic cavitation can carry the grime away.
De-Gas the Solvent Before Adding Brass
One of our readers, Eddy M. in Glasgow, Scotland writes: “I have read a couple of articles recently about ultrasonic cleaning of cases and not one has mentioned de-gassing the cleaning liquid before starting to clean items. As an engineer who traveled around for ten years servicing ultrasonic tanks I would like to point out that the cleaning liquid when first put into the tank has invisible dissolved air bubbles in it which will absorb ultrasonic energy until the liquid de-gasses. (Ten minutes in a powerful industrial tank — longer in a small hobby tank). You must let the tank run on its own for 20 minutes on the first use of the liquid to allow this to happen. Only after the new liquid or re-introduced liquid has been de-gassed will the tank give good results.”
Apply Dry-Lube Inside Case Necks
Jason Baney has found that Ultrasonic cleaning leaves the inside of the case-necks so “squeaky clean” that there is excess friction when seating bullets. On a fired case that has been cleaned conventionally (no ultra-sound), a thin layer of carbon remains to lubricate the bullet entry and exit. To restore that lubricity in cases cleaned with ultrasound, Jason applies a dry lube to the inside of his case necks. Jason prefers the $10.95 moly dry lube kit from Neconos.com. With this kit, small carbon steel balls transfer moly to the neck when you place your brass nose-down in the container.
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October 22nd, 2014
Our take on Bore-Store Gun sleeves is simple: They work great, so buy them and use them — for ALL your valuable firearms.
These thick, synthetic-fleece sacks cushion your guns, preventing nicks and scratches. The breathable fabric wicks away moisture, and the fibers are coating with corrosion inhibitors. I personally use Bore-Stores for in-safe storage with all my guns, and I have never had one of my guns rust inside a Bore-Store, even when I lived a stone’s throw from the ocean.
Bore-Stores are offered in a wide range of sizes, so you can find something to fit everything from a Snub-nosed revolver to a 32″-barrelled 50 BMG. Rifle-size Bore Stores can be purchased for $12.00 – $21.00 from Brownells. For long F-Class or tactical rifles, we recommend the 10″x52″ Scoped Shotgun Bag, Brownells item 132-000-003. You can also order direct from the Bore-Store manufacturer, Big Spring Enterprises, www.BoreStores.com. Big Spring will also craft custom sizes on request.
Consider Military-Style, Triple-Layer Bags for Long-Term Storage
While we prefer Bore-Stores for regularly-used guns, if you have heirloom firearms that will be kept in storage for very long periods without seeing any use, you may want to grease them up and place them in the thin, but rugged three-layer storage bags sold by Brownells. The bags are made from a three-layer laminate of polyester, aluminum, and polyethylene film, with a shiny silver exterior. Though the laminate is thin, the Brownells storage bags are puncture-resistant, and have a 0% moisture transmission rating so moisture can’t get inside. These bags are also resistant to petroleum-based chemicals and they won’t break down even in contact with soil or moisture.
Here’s one VITAL bit of advice for using these bags. Be absolutely sure, before you seal up the bags, that your guns are DRY and that all metal surfaces have been coated with an effective anti-corrosive, such as BoeShield T9 or Eezox. Brownells’ storage bags are inexpensive. A three-pak of 12″x 60″ rifle sacks (item 083-055-003WB) costs just $22.99 — under eight bucks a gun. That’s cheap insurance for rifles and shotguns that may cost thousands of dollars.
Get Your Guns Out of Foam-lined Cases — They Are Rust Magnets
Just about the worst thing you can do in the winter (short of leaving your rifle outside in the rain) is to store firearms in tight, foam-padded cases. The foam in these cases actually collects and retains moisture from the air, acting as the perfect breeding ground for rust.
Remember, those plastic-shelled cases with foam interiors are for transport, not for long-term storage. Don’t repeat the mistake of a wealthy gun collector I know. He stored four valuable Colt Single Action Army (SAA) revolvers in individual foam-padded cases, and locked these away in his gun safe. A year later, every one of his precious SAAs had rusted, some badly.
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October 19th, 2014
One of our readers asked “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.
Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:
“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ ASL or less. I’ll need about 29-30 MOA to get from 100 yard to 1000 yards with a Berger 155gr VLD @ 2960fps. By contrast, in Raton, NM, located at 6600′ ASL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.
Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”
As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect.
It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet amsl), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestral, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.”
You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.
Trajectory of Bullet fired at Sea Level
Trajectory of Bullet fired at 20,000 feet
if you want to learn more about all aspects of External Ballistics, ExteriorBallistics.com provides a variety of useful resources. In particular, on that site, Section 3.1 of the Sierra Manual is reprinted, covering Effects of Altitude and Atmospheric Pressure on bullet flight.
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October 17th, 2014
Can you guess what your next barrel will weigh? In many competition disciplines, “making weight” is a serious concern when putting together a new match rifle. A Light Varmint short-range Benchrest rifle cannot exceed 10.5 pounds including scope. An F-TR rifle is limited to 18 pounds, 2 oz. (8.25 kg) with bipod.
One of the heaviest items on most rifles is the barrel. If your barrel comes in much heavier than expected, it can boost the overall weight of the gun significantly. Then you may have to resort to cutting the barrel, or worse yet, re-barreling, to make weight for your class. In some cases, you can remove material from the stock to save weight, but if that’s not practical, the barrel will need to go on a diet. (As a last resort, you can try fitting a lighter scope.)
Is there a reliable way to predict, in advance, how much a finished barrel will weigh? The answer is “yes”. PAC-NOR Barreling of Brookings, Oregon has created a handy, web-based Barrel Weight Calculator. Just log on to Pac-Nor’s website and the calculator is free to use. Pac-Nor’s Barrel Weight Calculator is pretty sophisticated, with separate data fields for Shank Diameter, Barrel Length, Bore Diameter — even length and number of flutes. Punch in your numbers, and the Barrel Weight Calculator then automatically generates the weight for 16 different “standard” contours.
Calculator Handles Custom Contours
What about custom contours? Well the Pac-Nor Barrel Weight Calculator can handle those as well. The program allows input of eight different dimensional measurements taken along the barrel’s finished length, from breech to muzzle. You can use this “custom contour” feature when calculating the weight of another manufacturer’s barrel that doesn’t match any of Pac-Nor’s “standard” contours.
Smart Advice — Give Yourself Some Leeway
While Pac-Nor’s Barrel Weight Calculator is very precise (because barrel steel is quite uniform by volume), you will see some small variances in finished weight based on the final chambering process. The length of the threaded section (tenon) will vary from one action type to another. In addition, the size and shape of the chamber can make a difference in barrel weight, even with two barrels of the same nominal caliber. Even the type of crown can make a slight difference in overall weight. This means that the barrel your smith puts on your gun may end up slightly heavier or lighter than the Pac-Nor calculation. That’s not a fault of the program — it’s simply because the program isn’t set up to account for chamber volume or tenon length.
What does this mean? In practical terms — you should give yourself some “wiggle room” in your planned rifle build. Unless you’re able to shave weight from your stock, do NOT spec your gun at one or two ounces under max based on the Pac-Nor calculator output. That said, the Pac-Nor Barrel Weight Calculator is still a very helpful, important tool. When laying out the specs for a rifle in any weight-restricted class, you should always “run the numbers” through a weight calculator such as the one provided by Pac-Nor. This can avoid costly and frustrating problems down the road.
Credit Edlongrange for finding the Pac-Nor Calculator
Caution: Same-Name Contours from Different Makers May Not be Exactly the Same
One final thing to remember when using the Barrel Weight Calculator is that not all “standard” contours are exactly the same, as produced by different barrel-makers. A Medium Palma contour from Pac-Nor may be slightly different dimensionally from a Krieger Medium Palma barrel. When using the Pac-Nor Barrel Weight Calculator to “spec out” the weight of a barrel from a different manufacturer, we recommend you get the exact dimensions from your barrel-maker. If these are different that Pac-Nor’s default dimensions, use the “custom contour” calculator fields to enter the true specs for your brand of barrel.
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October 13th, 2014
by Philip Mahin, Sierra Bullets Ballistic Technician
This article first appeared in the Sierra Bullets Blog
The ANSI / SAAMI group, short for “American National Standard Institute” and “Sporting Arms and Ammunition Manufacturers’ Institute”, have made available some time back the voluntary industry performance standards for pressure and velocity of centerfire rifle sporting ammunition for the use of commercial manufacturers. [These standards for] individual cartridges [include] the velocity on the basis of the nominal mean velocity from each, the maximum average pressure (MAP) for each, and cartridge and chamber drawings with dimensions included. The cartridge drawings can be seen by searching the internet and using the phrase ‘308 SAAMI’ will get you the .308 Winchester in PDF form. What I really wanted to discuss today was the differences between the two accepted methods of obtaining pressure listings. The Pounds per Square Inch (PSI) and the older Copper Units of Pressure (CUP) version can both be found in the PDF pamphlet.
Image by ModernArms, Creative Common License.
CUP Pressure Measurement
The CUP system uses a copper crush cylinder which is compressed by a piston fitted to a piston hole into the chamber of the test barrel. Pressure generated by the burning propellant causes the piston to move and compress the copper cylinder. This will give it a specific measurable size that can be compared to a set standard. At right is a photo of a case that was used in this method and you can see the ring left by the piston hole.
PSI Pressure Measurement
What the book lists as the preferred method is the PSI (pounds per square inch or, more accurately, pound-force per square inch) version using a piezoelectric transducer system with the transducer flush mounted in the chamber of the test barrel. Pressure developed by the burning propellant pushes on the transducer through the case wall causing it to deflect and make a measurable electric charge.
Q: Is there a standardized correlation or mathematical conversion ratio between CUP and PSI values?
Mahin: As far as I can tell (and anyone else can tell me) … there is no [standard conversion ratio or] correlation between them. An example of this is the .223 Remington cartridge that lists a MAP of 52,000 CUP / 55,000 PSI but a .308 Winchester lists a 52,000 CUP / 62,000 PSI and a 30-30 lists a 38,000 CUP / 42,000 PSI. It leaves me scratching my head also but it is what it is. The two different methods will show up in listed powder data[.]
So the question on most of your minds is what does my favorite pet load give for pressure? The truth is the only way to know for sure is to get the specialized equipment and test your own components but this is going to be way out of reach for the average shooter, myself included. The reality is that as long as you are using printed data and working up from a safe start load within it, you should be under the listed MAP and have no reason for concern. Being specific in your components and going to the load data representing the bullet from a specific cartridge will help get you safe accuracy. [With a .308 Winchester] if you are to use the 1% rule and work up [from a starting load] in 0.4 grain increments, you should be able to find an accuracy load that will suit your needs without seeing pressure signs doing it. This is a key to component longevity and is the same thing we advise [via our customer service lines] every day. Till next time, be safe and enjoy your shooting.
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