Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 2 by Bryan Litz forBerger Bullets. Part One of this series focused on the importance of COAL in terms of SAAMI standards, magazine lengths, seating depths, and pressure levels. Another measure of length for loaded ammunition is highly important to precision, namely Cartridge Base to Bullet Ogive Length (CBTO).
Figure 2. Chamber throat geometry showing the bullet jump to the rifling or lands.
Look at Figure 2. Suppose the bullet was seated out of the case to the point where the base of the bullet’s nose (ogive) just contacted the beginning of the riflings (the lands) when the bolt was closed. This bullet seating configuration is referred to as touching the lands, or touching the riflings and is a very important measurement to understand for precision hand-loading. Due to the complex dynamics of internal ballistics which happen in the blink of an eye, the distance a bullet moves out of the case before it engages the riflings is highly critical to precision potential. Therefore, in order to systematically optimize the precision of his handloads, it’s critically important that the precision hand-loader understands how to alter bullet seating depth in relation to the barrel rifling. Part of the required knowledge is understanding how to accurately and repeatably measure the Cartridge Base To Ogive (CBTO) dimension. This is explained in the FULL ARTICLE.
Bryan Litz offers an extended discussion on how to measure CBTO using different tools and methods, including the Hornady OAL gauge. You can read this discussion in the full article found on the Berger Bullets website. CLICK HERE to Read Full Article.
Why Not Use CBTO as a SAAMI Standard?
If CBTO is so important to rifle accuracy, you might ask, “Why is it not listed as the SAAMI spec standard in addition to COAL?” There is one primary reason why it is not listed in the standard. This is the lack of uniformity in bullet nose shapes and measuring devices used to determine CBTO.
Figure 4. Two different bullet shapes, seated to the same CBTO length, but different COAL. Note the shiny scratches on the bullets made by the comparator tool which indicates a point on the bullet ogive near where the ogive will engage the riflings.
Benefits of Having a Uniform CBTO
There is another aspect to knowing your CBTO when checking your COAL as it pertains to performance. With good bullets, tooling, and carefully-prepared cases you can easily achieve a CBTO that varies less than +/- .001″ but your COAL can vary as much as .025″ extreme spread (or more with other brands). This is not necessarily bad and it is much better than the other way around. If you have a CBTO dimension that varies but your COAL dimension is tight (within +/- .002″) then it is most likely that your bullet is bottoming out inside the seater cone on the bullet tip. This is very bad and is to be avoided. It is normal for bullets to have precisely the same nose shape and it is also normal for these same bullets to have nose lengths that can vary as much as .025″.
Summary of Cartridge Base To Ogive (CBTO) Discussion
Here are four important considerations regarding bullet seating depth as it relates to CBTO:
1. CBTO is a critical measurement to understand for handloaders because it’s directly related to precision potential, and you control it by simply setting bullet seating depth.
2. Tools and methods for measuring CBTO vary. Most of the measurement techniques have pitfalls (which may give rise to inconsistent results) that you should understand before starting out.
3. A CBTO that produces the best precision in your rifle may not produce the best precision in someone else’s rifle. Even if you have the same rifle, same bullets, same model of comparator gauges, etc. It’s possible that the gauges are not actually the same, and measurements from one don’t translate to the same dimension for another.
4. Once you find the CBTO that produces the best precision in your rifle, it’s important to allow minimal variation in that dimension when producing quality handloads. This is achieved by using quality bullets, tooling, and properly preparing case mouths and necks for consistent seating.
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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We recommend that all hand-loaders have a couple reliable reloading manuals as reference guides. Berger, Hornady, and Sierra all offer well-respected load manuals. These can provide starting load information for a wide variety of cartridge types and bullet selections. We do like to cross-check any printed load recipes with current online data, to ensure you have the latest info.
Along with a good load manual, those getting started in metallic cartridge reloading can benefit from a good basic reloading treatise. There’s a new intro guide from the publishers of Gun Digest.
The New Gun Digest Shooter’s Guide To Reloading, by Phillip Massaro, was created for shooters new to reloading. This is a good starting point for those who want to learn to hand-load safely and efficiently. Hundreds of photos illustrate the text — and we all know a picture can be worth a thousand words.
After discussing the benefits of hand-loading, Massaro’s book covers the basics of metallic cartridge reloading, step by step. Along the way Massaro recommends appropriate presses and tools for reloading both pistol and rifle cartridges. Massaro also explains the variations in bullet and powder types, and how they affect ballistics. In addition, Massaro includes a “Specialty Situations” chapter that reveals common reloading mistakes and issues and offers practical solutions. This section on avoiding common mistakes is one of book’s best features. We wish all reloading guides had a similar section.
Editor’s NOTE: This book will be released next week. Accordingly, we have not seen the final, printed version yet. At $14.79, the Gun Digest Shooter’s Guide to Reloading is relatively inexpensive. The sample chapters we reviewed provided good basic information in a well-organized fashion. Certainly, we would not tell advanced reloaders and/or competition shooters to rush out and buy this book. However, for folks getting started in hand-loading, this resource should be helpful.
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When you need ammo fast — lots of ammo, it’s hard to beat a progressive reloading press for output. We use progressive presses to load handgun ammo and .223 Rem cartridges for varmint safaris. With good dies, and proper press set-up, today’s progressive presses can produce surprisingly uniform and accurate ammo. No, you won’t see Benchrest Hall-of-Famers loading PPC cartridges on progressives. However, if you need 1000 rounds for your next prairie dog adventure, you should consider getting a progressive. Below you can see a Hornady Lock-N-Load AP configured to load .308 Winchester in bulk.
Proper Brass Prep
Just like a good paint job requires good prep work, great rifle ammo requires good brass prep. In order to make sure your rifle loading goes smoothly, make sure to perform the following brass prep steps:
Clean the brass (tumble, ultrasonic, etc.)
Inspect brass for cracks, deep dents, etc.
For military brass: de-prime, ream/swage primer pockets, size with small-base sizer die (small base usually optional).
Measure brass length — if too long, size and then trim.
Final inspection before loading.
Cleaning primer pockets may be something you’ll consider (I don’t clean primer pockets except for rare cases or match ammo).
Smooth and Steady Pace
Since you’re loading rifle ammunition on a progressive, you’re already saving a load of time, so there’s no need to rush things! Attention to detail is super-important for safety and for good results. Always keep an eye on powder level (goes down FAST) and what’s happening at each station.
The Right Press and Press Setup
Look for a heavy-duty, well-built press that will stand up to rifle loading. You’ll also want to make sure your powder measure will have the proper capacity (~25 grains for .223, ~50 grains for 308). If you are bulk reloading, ensure you have enough stations for sizing, charging, powder check, bullet feed, bullet seating, and (optional) bullet crimp.
More Ultimate Reloader Resources for Users of Progressive Presses:
If you haven’t visited the Norma website recently, you should click over to www.norma.cc/en/ (the ‘en’ is for English version). There you will find Norma’s “Ammo Academy”, a technical resource that provides information on: Ballistics, Powder Storage, Barrel Wear, and Bullet Expansion. In addition, the Ammo Academy now links to Norma’s Reloading Data Center, where you’ll find loads for nearly 70 cartridge types including: .223 Rem, .22-250, 6mmBR Norma, 6XC, 260 Rem, 6.5-284, 6.5×55, 7mm-08, .270 Win, .284 Win, .308 Win, .30-06, 300 Win Mag, .338 Lapua Mag and dozens more.
The Ammo Academy’s Ballistics section contains some fascinating technical facts:
After the trigger is pulled, it takes around 0.005 seconds before the firing pin reaches the primer.
From the firing of the primer it takes 0.0015-0.002 seconds until the bullet exits the muzzle.
When the bullet leaves the muzzle, the hot gases surround and overtake the bullet, continuing the acceleration for a few centimeters.
Because the barrel is always angled slightly upwards, the bullet’s flight starts about 3-5 cm below the line of sight.
Norma also offers some good advice about Powder and Cartridge Storage:
To maintain the product quality for as long as possible, you have to keep the powder in a suitable place under suitable conditions. Where possible, store the powder at a constant temperature, ideally between 12 and 15°C (54°F to 59°F), and a relative humidity of 40–50%. If the air is too dry, it will dry out the powder, which will cause the pressure to be higher, thus affecting performance. Also make sure that you close the powder container properly afterwards. Cartridges should be stored under the same ambient conditions to maintain their quality.
The February 2013 edition of Shooting Sports USA magazine has an interesting feature by Glen Zediker. In this Transporting Success, Part I article, Zediker explains the advantages of loading at the range when your are developing new loads or tuning existing loads. Glen, the author of the popular Handloading for Competition book, discusses the gear you’ll need to bring and he explains his load development procedure. In discussing reloading at the range, Glen focuses on throwing powder and seating bullets, because he normally brings enough sized-and-primed brass to the range with him, so he doesn’t need to de-prime, re-size, and then re-prime his cases.
Zediker writes: “Testing at the range provides the opportunity to be thorough and flexible. You also have the opportunity to do more testing under more similar conditions and, therefore, get results that are more telling. Once you are there, you can stay there until you get the results you want. No more waiting until next time.”
Zediker starts with three-shot groups: “I usually load and fire three samples [with] a new combination. I’ll then increase propellant charge… based on the results of those three rounds, and try three more. I know that three rounds is hardly a test, but if it looks bad on that few, it’s not going to get any better.”
Glen reminds readers to record their data: “Probably the most important piece of equipment is your notebook! No kidding. Write it down. Write it all down.”
There’s More to the Story…
Editor’s Note: In Zediker’s discussion of loading at the range, he only talks about throwing powder and seating bullets. In fact, Glen opines that: “there is little or no need for sizing.” Well, maybe. Presumably, for each subsequent load series, Zediker uses fresh brass that he has previously sized and primed. Thus he doesn’t need to de-prime or resize anything.
That’s one way to develop loads, but it may be more efficient to de-prime, re-size, and load the same cases. That way you don’t need to bring 50, 80, or even 100 primed-and-sized cases to the range. If you plan to reload your fired cases, you’ll need a system for de-priming (and re-priming) the brass, and either neck-sizing or full-length sizing (as you prefer). An arbor press can handle neck-sizing. But if you plan to do full-length sizing, you’ll need to bring a press that can handle case-sizing chores. Such a press need not be large or heavy. Many benchresters use the small but sturdy RCBS Partner Press, an “O-Design” that costs about $79.00. You may even get by with the more basic Lee Precision Compact Reloading Press, shown in Zediker’s article. This little Lee press, Lee product #90045, retails for under $30.00.
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Do you own an RCBS electronic powder dispenser? If you do, take the time to watch this ChargeMaster Tuning video from 8541 Tactical. This nine-minute video demonstrates how to re-program your Chargemaster to “tune” the dispensing process. The video shows the exact programming procedures to follow, step-by-step. Some folks want a faster powder flow — others tune their machines for a more reliable drop (with fewer over-runs). One cheap and popular modification is to insert a 1″-long section of a McDonald’s straw in the ChargeMaster’s silver dispensing tube. This works surprisingly well to smooth kernel drop and prevent “clumping” that can cause an over-charge. The McDonald’s straw MOD is demonstrated in this video, starting at the 6:22 mark.
Large-Diameter Dispensing Tube Mod
Many folks have had success with the McDonald’s straw modification demonstrated in the above video. However, some folks would like to get even better flow performance (with virtually no clumping). Forum Member Frank B. has come up with a new option using a brass hose fitting with a large outside diameter. The hose fitting (with tape wrapped around the barbed nose section) is placed inside the RCBS dispensing tube (be sure to have some kind of wrap — you don’t want metal-on-metal). Here’s how the unit looks installed:
Frank tells us: “I have found a cure for the over-throw problem. It is a simple 1/4″ barbed hose nipple. I wrapped a couple layers of tape around the barbed end for a snug fit. With this in place, I have thrown 100+ charges of Varget without a single overthrow. The ID of the barbed end needs to be approximately 3/16″ to feed a steady flow. This works because of the larger ID at the drop.”
Frank adds: “You can see in the photo that the powder is not stacking up. You can watch it drop one grain at a time. Hope this will take the aggravation out of your case charging.” For best performance with this brass fitting MOD, we recommend de-burring and smoothing out the front edge of the brass fitting over which the kernels drop.
Brass fitting mod suggested by Boyd Allen. We welcome reader submissions.
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We have all been there…..you place a piece of tumbled brass in the shell-holder of your press, raise it into the die, and suddenly it is like somebody hit the brakes. The case is stuck in the die. Your first instinct is to reverse it out. You crank on the handle, and BANG! The rim rips off the case head and you are looking at a piece of brass stuck in the die.
A stuck case is one of the boo-boos that all of us reloaders have faced from time to time. If proper lubrication is applied, then it should not be a problem. No matter if you are a seasoned reloader or new to it, this situation can happen. Take your time, use the proper procedures, and you will be back in business in no time! This article explains how to avoid stuck cases (through proper lubrication) and how to use a stuck case removal system.
What Causes Stuck Cases
One of the first common mistakes reloaders face is the stuck case. It can be caused by too much or too little lube. Too much and a vacuum can be formed causing the case to become suctioned into the die. Too little lube and friction is the culprit. So what is the cure? There is no exact cure, but the best lube that we have found so far is just a dab of Imperial Sizing Die Wax on your fingers and applied in a thin coat on the body of the case, not the shoulder or neck. Too much of this wax can cause the vacuum effect, or can eventually load your die up with gobs of residue. If it is applied to the shoulder area, or the leftover wax moves up into the shoulder region of the die, you will see dents or dimples in the shoulder. [AccurateShooter.com Editor's Note: For normal full-length sizing of small cases such as 220 Russian/PPC, 6mmBR, 6.5 Grendel, or 6.5x47 Lapua we recommend Ballistol (aerosol) lube. It is very slippery, goes on very thin, and does not gum up the die.]
A great way to ensure that your dies are clean is to use a simple chamber mop with a dab of your favorite solvent on it and clean out the die. Be sure all of the solvent is out after cleaning by spraying the die out with Quickscrub III or use a clean chamber mop. If you are storing your dies, you can apply a thin coat of a good oil to protect the steel such as TM oil or Starrett M1 Spray.
Using a Stuck Case Removal Kit
If you do stick a case in your die there are a few good stuck case removal kits available. Each one works in a similar fashion. I have found the Hornady kit very effective and easy to use.
Basically what you do is remove the die from the press. Unscrew the decapping assembly and pull it out as far as you can. You then need to drill/tap threads into the stuck case head (this is why it is suggested to unscrew the decapping assembly as far as you can to get it clear of the drill bits). Once this is done screw the die back into the press. You then install the included shellholder attachment on the shellholder ram, and thread it into the case via a small wrench. With some elbow grease you can reverse the stuck case out of the die with the leverage of the press, and not damage the die.
However if the case is stuck….REALLY stuck, you may pull out the threads on the case and you are still left with a stuck case in the die without any way to pull it out. If the case is really difficult to remove even with the use of a stuck case removal kit, do not try to be Hercules with the press ram. Here is a trick that may work. Take the die with the stuck case and place it in your freezer for a couple of hours. Then repeat the removal with the cold die. The freezing temperatures may cause the brass to contract, and make removal easier. If this does not work it is recommended to send it to the die manufacturer. They will be able to remove the case without damaging the die.
Another fix if you can remove the decapping assembly completely is to use a tap hammer and a punch or small wooden dowel to knock the stuck case out. This isn’t the best way since it is very possible that you will damage the die internally or externally on the threads, or both. Send the die to the manufacturer to have this done properly. You will be happier in the long run.
In our Shooters’ Forum, many questions are asked about QuickLOAD software — how to get best results, how to use the advanced features, how to adjust for temperature and so on. To help answer those questions, here’s a short feature we first ran during SHOT Show 2012. You can also CLICK HERE for a very detailed explanation of QuickLOAD in our main site.
At SHOT Show, we had the chance to meet with German software engineer Hartmut Broemel, creator of QuickLOAD software. This software program, while not a substitute for conventional load manuals, allows shooters to evaluate a wide range of powders and bullets, comparing potential loads on the basis of predicted pressures, velocities, load density and projectile in-barrel time.
We took the opportunity, in the video below, to explain some of the fine points of QuickLOAD for our members. QuickLOAD, sold by Neconos.com, helps reloaders understand how changing variables can affect pressures and velocities. It can predict the effect of changes in ambient temperature, bullet seating depth, and barrel length.
In the video below we explain how to adjust the program for true case capacity, bullet seating into the lands, and other important factors. If you are a new QuickLOAD user, or are contemplating buying the $152.95 program, you should watch the video. The program isn’t perfect, but it can accelerate the load development process, and it can save you money by narrowing down the list of appropriate powders for your cartridge.
No other product currently available to serious reloaders offers as much predictive power as QuickLOAD, and you’ll find your money well spent just for the vast collection of data on bullets and cartridges. With a couple mouse-clicks you can instantly get the specifications of hundreds of bullets and cartridges. Likewise, in a matter of seconds, you can compare load density for a half-dozen powders, or compare the projected velocities of one cartridge versus another.
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One of our Forum members complained that he wasn’t able to set his primers flush to the rim. He tried a variety of primer tools, yet no matter what he used, the primers still didn’t seat deep enough. He measured his primers, and they were the right thickness, but it seemed like his primer pockets just weren’t deep enough. He was mystified as to the cause of the problem.
Well, our friend Boyd Allen diagnosed the problem. It was the decapping rod. If the rod is adjusted too low (screwed in too far), the base of the full-diameter rod shaft (just above the pin) will contact the inside of the case. That shaft is steel whereas your case is brass, a softer, weaker metal. So, when you run the case up into the die, the shaft can actually stretch the base of the primer pocket outward. Most presses have enough leverage to do this. If you bell the base of the primer pocket outwards, you’ve essentially ruined your case, and there is no way a primer can seat correctly.
The fix is simple. Just make sure to adjust the decapping rod so that the base of the rod shaft does NOT bottom out on the inside of the case. The pin only needs to extend through the flash hole far enough to knock the primer out. The photo shows a Lyman Universal decapping die. But the same thing can happen with any die that has a decapping rod, such as bushing neck-sizing dies, and full-length sizing dies.
Whenever you use a die with a decapping pin for the first time, OR when you move the die to a different press, make sure to check the decapping rod length. And it’s a good idea, with full-length sizing dies, to always re-check the height setting when changing presses.
Lee Universal Decapping Die on SALE for $9.89
Speaking of decapping tools, Midsouth Shooters Supply sells the Lee Universal Decapping Die for just $9.34 (item 006-90292), a very good deal. There are many situations when you may want to remove primers from fired brass as a separate operation (prior to case sizing). For example, if your rifle brass is dirty, you may want to de-cap before sizing. Or, if you load on a progressive press, things will run much more smoothly if you decap you brass first, in a separate operation. The Lee Universal Decapping Die will work with cartridges from 17 Fireball all the way up to 45-70. However, NOTE that the decapping pin supplied with this Lee die is TOO LARGE for LAPUA 6.5×47, 6BR, 220 Russian, and Norma 6 PPC flash holes. Because the pin diameter is too large for these brass types, you must either turn down the pin, or decap with a different tool for cases with .059″ flash-holes. Otherwise, the Lee Decapping Die works well and it’s a bargain.
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When your cases become hard to extract, or you feel a stiff bolt lift when removing a cartridge, it’s probably time to full-length size your cases, and “bump” the shoulder back. With a hunting load, shoulder bumping may only be required every 4-5 loading cycles. Short-range benchrest shooters, running higher pressures, typically full-length size every load cycle, bumping the shoulder .001-.002″. High Power shooters with gas guns generally full-length size every time, and may need to bump the shoulders .003″ or more to ensure reliable feeding and extraction.
Use Shims for Precise Control of Shoulder Bump
Some shooters like to set the “default” position for their full-length die to have an “ample” .003″ or .004″ shoulder bump. When they need less bump, a simple way to reduce the amount of shoulder movement is to use precision shims in .001″ (one-thousandth) increments.
Mats Johansson writes: “I’ve been using [shims] since Skip Otto (of BR fame) came out with them. I set up my dies with the .006″ shim, giving me the option of bumping the shoulder a bit more when the brass gets old and hardens while still having room to adjust up for zero headspace, should I have missed the original setup by a thou or two. Hunting rounds can easily be bumped an extra .002-.003″ for positive, no-crush feeding. Being a safety-oriented cheapskate, I couldn’t live without them — they let me reload my cases a gazillion times without dangerous web-stretching. Shims are a must-have, as simple as that.”
Sinclair Int’l offers a 7-piece set of Die Shims that let you adjust the height of your die (and thereby the amount of bump and sizing) in precise .001″ increments. Sinclair explains: “Some handloaders will set their die up to achieve maximum sizing and then progressively use Sinclair Die Shims between the lock ring and the press head to move the die away from the shellholder. Doing this allows you to leave the lock ring in the same position. These shims are usually available in increments of .001″ and work very well.”
Seven Shims from .003″ to .010″
Sinclair’s $12.49 Die Shim Kit (item 22400) includes seven shims in thicknesses of .003, .004, .005, .006, .007, .008, and .010. For ease of use, shim thickness is indicated by the number of notches cut in the outer edge of each shim. Even without looking you can “count” the notches by feel.
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Do you use bushings to size your case-necks? Are you assuming that your bushings are actually round on the inside, with a hole that’s centered-up properly? Well you may be in for an unpleasant surprise, based on what our friend Jim de Kort recently discovered. Jim was concerned about the run-out on his brass. His cases went into his bushing-equipped FL die pretty straight, but came out of the die with up to .004″ run-out. “What gives?”, Jim wondered. “Could the problem be the bushings themselves?”
To answer that question, Jim decided to examine his bushings. Using an Accuracy One Wheel-drive concentricity gauge, Jim checked out some of his neck bushings. What he discovered may surprise you…
Neck Bushing Flaws Revealed
Trust no one… — Jim de Kort
Jim writes: “I measured the concentricity of my 6BR rounds today. I noticed they went into the neck-bushing equipped full-length sizing die with <.001" deviation but came out with .003-.004". The culprit, it appears, was the bushing itself. Without it the cases stayed within .0005" to .001" deviation, so something was happening with the bushing.
One bushing had .00025" deviation on the outside, yet almost .003" on the inside, so it is crooked. But even when using a bushing that is within .001" I still get .003" runout after sizing. I repeated the same procedure for my 6x47 and got the same results. When using the bushing, concentricity suffers a lot."
Before we bash the bushing-makers, we must acknowledge that many different things can contribute to excessive run-out and/or mis-alignment of case-necks. We don’t have all the answers here, and Jim would be the first to say that some mysteries remain. Still, these are interesting results that give all precision hand-loaders something to think about.
Jim Borden also offers this tip: “Check the trueness of the face of the die cap. That has more to do with trueness than the bushing. Also check perpendicularity of hole in bushing to top surface. When I was making dies, the cap was made by threading and facing the threaded tenon in same setup.”
Editor’s Comment: Many people have great results with neck-bushing dies, but Jim isn’t the only fellow who has seen some very odd results. I personally employ honed, non-bushing dies for many of my chamberings. These non-bushing dies (with the necks honed for .002-.003″ neck tension) produce extremely straight ammo, with run-out consistently under .0015″.
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