MAGALY GASTÉLUM
8. HA IDO A PILLAR Y OTROS FORMULEMAS. CARMEN MARTÍN CUADRADO
HOW TO CARE FOR CARTRIDGE CASES
Bench rest shooters sometimes use one case, and frequently use a set of 15-20 cases during a match. Offhand shooters will use many cases during a match. What follows below applies to both bench rest and offhand shooters.
Always chamfer the inside and outside of the case mouth to remove burrs and sharp edges. Tools are available from RCBS, Lee and many others.
Always clean the primer pockets when repriming. This can be done with one of the available tools, with a screwdriver, with the scraper built into the Simmons style de/reprimer, or with a small Allen wrench.
Always wipe off each cartridge case before reloading. Make sure to clean both the forward edge of the rim and the base of the case. Wipe off each cartridge case after firing at the bench. This will alert you to blow-by caused by the case neck not sealing to the chamber wall.
Some bench rest shooters segregate cases by weight. The theory is that weight variation means case volume variation means velocity variation means less accuracy. Selecting a dozen cases with the same weight isn¶t difficult and may increase accuracy.
Primer pocket uniforming is the process of making each primer pocket the same depth.
The tool used is called a ³primer pocket uniformer´; these tools are available from Sinclair, Lyman, Midway and others. I uniform all primer pockets. I can¶t prove it helps, but it can¶t hurt.
Flash hole deburring is done with a ³flash hole deburrer´ available from Sinclair, Lyman Midway and others. This is done from the mouth of the case, and removes any burrs that have been thrown up when the flash hole is pierced in the case. I deburr flash holes on all cases. I can¶t prove that it increases accuracy, but I do know that there is a wide variation in the amount of material removed from case to case in the same lot.
HOW TO TRIM CASES TO LENGTH AND WHY
We trim cases to the same length for several reasons.
In rifles or rifle-like single shot pistols, cases that are too long can cause high pressures and perhaps damage the gun.
Variations in case length cause variations in case mouth belling with an "M" die.
Variations in case length equal variation in seating depth, bullet pull and (perhaps) accuracy.
In revolvers, the same ³M´ die problems exist in addition to problems with crimping the bullets.
Auto-loading pistols like the 1911 Colt and the P08 Luger headspace on the case mouth.
This means that the cartridge goes into the chamber until the case mouth meets a step in the chamber. Thus case length for these pistol cartridges is important, and cases should be trimmed to the specified length to assure proper functioning of the pistol.
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"Joe, this paragraph is in error. The 30 Carbine is the only cartridge that I know of that actually headspaces on the case mouth. Its OAL is important; if it is too long, the round will not chamber and if too short the round may not fire the primer. I check the OAL of fired cases and trim to a specific OAL (for my rifle) so that the FLS case lengthening will not be too long, approximately 0.018´ longer after FLS. When trimmed as such, I keep the brass separate from
firing (+/-0.018´). The 45 ACP and 9MM PB do have a chamber cut for case mouth headspace, but most brass is too short to work in that manner. The extractors on these pistols control
headspace. Some 9MM brass can be too long as there are several versions of 9MM OAL¶s besides the 9X19MM Luger, the 9X21 and 9X23MM (perhaps another longer one) could be too long. The 9X18 (380 ACP) might fit and fire in a 9X19 chamber."
Bill McGraw
The paragraph above, beginning "Auto-loading pistols like..." describes the planned or theoretical method of headspacing. See "1911 HEADSPACING METHOD--Norm Johnson" for more. I don't know which of the guns (and there are many) that supposedly headspace on the case mouth do, in reality, headspace on the case mouth. I believe that in this context, Case Trimming, it is proper to recommend trimming these cartridge cases to the "book" length. Other procedures are for the advanced caster/reloader.
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Case trimming is done to get cases to the "right" length, to make the case mouths square with the case long axis, and more importantly, to get cases to the same length. The right length is about ten thousandths of an inch less than the chamber length. The chamber in your barrel has a step at the forward end, where the cartridge case is supposed to end. The step is to a smaller diameter called the "throat", which is a little over bullet size. We don't want the case so long that its mouth interferes with the step, because that interference can cause large increases in pressure.
If the case is too long it will jam into the bullet as the cartridge is put into the gun, and this jamming will raise pressures, causing inaccuracy at the least and a blown up gun at the worst.
WHEN TO TRIM CASES:
Ken Mollohan
ALL cases should be checked for correct length before loading, including unfired, factory new brass.
All cases in a batch should also be spot checked after firing and before sizing by simply trying to insert a jacketed bullet into the mouth of the unsized case by hand. This is a check to see if the case neck is too thick, or if it¶s elongated to the point that the mouth is crimped by the end of the chamber. Thick necks are rare indeed unless you¶ve had to form your cases from another cartridge, and this can / should be corrected by neck turning or reaming as part of the forming process.
In either case, the slightest resistance indicates that the cases are not safe to load until the problem has been corrected. Usually, the entire batch of cases needs to be trimmed again. If trimming solves the problem, the jacketed bullet will go in easily and the case is OK to load - at least from this aspect of case inspection. If the jacketed bullet still encounters some resistance, try deburring the case mouth and/or turning the neck.
This elongating growth is an absolutely unavoidable result of loading and shooting. The pressure from firing the load causes the brass case to expand, exactly as a balloon expands from the pressure of your lungs. When you resize the case, the expanded brass is squeezed down and elongated for much the same reason that toothpaste comes out when you squeeze the tube.
How to minimize trimming:
While some case growth is unavoidable, there are ways to minimize the problem, and even eliminate it for all practical purposes. Since the elongation occurs when the case is sized
down to a smaller diameter, the way to reduce elongation is to reduce sizing. There are several ways to do this:
1. Use moderate pressure loads. Just as higher pressure will make the balloon expand more, so will the case expand more with higher pressure loads. Use enough pressure to get the job done, but you don¶t need to use more than that. Higher expansion means more elongation when the case is sized.
2. When you size, don¶t over-do the process. The purpose for sizing is to make the case small enough to operate (feed, chamber, etc) easily in your gun. But most guns will work fine with cases that have been only partially sized. Instead of screwing your sizing die down hard against the shell holder, back it off a turn or two and see if the case still chambers easily. Less sizing equals less elongation of the case. The less one sizes, the less one will need to trim. Partial sizing, or neck sizing alone is frequently practiced to provide better centering of the round, but it has the advantage of minimizing the working and elongation of the case as well.
My practice is to adjust dies to size cases until they will chamber freely, and then screw the sizing die down 1/4 turn more, to compensate for the occasional case with more spring-back than usual. The only real reasons for full length sizing are if your chamber is not round (very rare) or the ammo needs to fit several different rifles.
3. With moderate loads and modern, relatively precise chambers, most guns will readily accept their own fired cases without any sizing at all. If so, don¶t bother to size them!
Get a neck sizer and reduce only the neck so the bullet will be held firmly. In principle, this will also result in some slight elongation, but for all practical purposes, I find that no trimming is necessary for neck sized cases. Oh, I still check an occasional case with a jacketed bullet, just in case, but I have yet to find a problem.
Note: The brass that you trim from the end of the neck doesn¶t appear by magic, nor does it grow like grass. The elongation of the brass case is at the expense of the thickness of the brass wall thickness. Every time you size a case, it is a scientific fact that its walls are slightly thinner than they were the last time you sized it. And so is the safety factor of your load. My personal recommendation is that you keep track and do not trim a batch of cases more than twice. With moderate loads, they¶ll last almost forever before they need a third trimming. At that point, you¶ve gotten your money¶s worth from them. Consider the cost of replacement brass as a very cheap insurance premium.
Ken
Case Length Measuring Tools
The McMillin-Hyer case length gauge is a NO GO gauge. If the case fits in the gauge, it is not too long. If the case does not fit in the gauge, it is too long and must be discarded or trimmed to length. Case length can also be measured with a dial or vernier caliper. Precision dial calipers are probably the best tool to use, are not overly expensive, and may be used for many other measurements.
Case Trimmers These vary from the simple Lee tool to complex powered machines. The Lee tool works perfectly, satisfies the needs of the beginner inexpensively, but is not adjustable.
I use a Forster Case Trimmer with accessories for case neck turning. This tool does a fine job of trimming cases to length, and turning case necks.
CASE LENGTH VS. ACCURACY
In the Nov./Dec. 2001 ASSRA Journal article: ³The Importance of Case Length in Cast Bullet Accuracy´, the author stated that short cases yield less accuracy than cases close to maximum length with cast bullets. The mechanism proposed is that the unsupported bullet in the gap between case end and chamber end will be expanded by the firing pressure, then the expanded section will be swaged down as the bullet moves through the throat-and the expansion/swaging will be uneven and cause inaccuracy. This article opened up a potential accuracy-improving easy and inexpensive shortcut. The article did not include any supporting data, so I imagined that what was put forth was a hypothesis.
To test this hypothesis I needed a rifle that shot fixed ammunition at high enough pressures, with sufficient accuracy, and for which extra long cases could be made or found.
The only rifle available to me that met these criteria was a Savage Tactical rifle with synthetic stock in 300 Winchester Magnum, fitted with a Weaver 3-9X telescopic sight. I owned this rifle for about four years, and it was reasonably accurate with cast lead bullets at slower velocities, 1200-1500 fps.
(We are told, and I believe, that cases that are too long will jam bullet and case neck into the throat of the rifle and cause very high pressures on firing.)
Pressure must be sufficient to expand the bullet into the space left by the short case. Expansion of the bullet under the gas pressure on firing is sometimes called "obturation".
In a private communication with the author, he said ³« obturation of lead-alloy bullets occurs at about 1500 psi times each Brinnel hardness point, e.g., a Brinnel hardness 10 bullet requires about 15,000 psi peak chamber pressure to achieve sufficient obturation to essentially fully seal the bore´
With wheel weights reported at 9-12 BHN, the pressure required to obturate would be 13,500 to 18,000 psi.
A pressure of greater than 18,000 psi was required. The Lyman Cast Bullet Handbook, third edition, shows a 187 grain 311334 bullet in the 300 WM with 17.5 grains of Unique at 1605 FPS and 26,400 psi. The load given below of a 208 grain bullet and 17 grains of Unique should produce at least this pressure, which exceeds the obturation threshold.
After several weeks of experimentation I found a load that shot accurately at higher velocity:
The 311299 bullet was cast of newly melted wheel weights, weighing 208.5 +/-.5 grains, sized in a .314´ die, lubed with the NRA alox-beeswax formula and gas checked (Hornady).
This bullet has three bands and two lube grooves along with the gas check shank. As loaded, the first band is out of the case with none/little of the first lube groove exposed.
17 grains of Unique was used with no filler, Remington L.P. #2 1/2 primers, LOA = 3.455´.
I loaded one case at the range, sizing the neck in a Lee sizer, expanding the neck in a Lyman ³M´ die and seating the bullet with the Lee loader.
I used this load and loading method for all groups shot in this test.
Extra long cases were made from Federal 300 H&H Magnum cases full-length sized in 300 WM dies and trimmed to about 2.660´.
The chamber would accept a case of 2.648´, .028´ longer than the published case length and .033´ longer than the trim-to length.
Being chicken, I trimmed the cases to 2.643´. After extensive firing, the cases measured 2.621" to 2.630´. What happened was that the tapered 300 H&H case had blown out to fill the chamber and shortened during firing.
The first test with short cases.
On March 13, 2002, using the load noted above and one R-P case measuring 2.605´ long, I shot five 5 shot 100 yard groups that averaged 1.132":
The test with a long case made from a 300 H&H Magnum case
On March 21, 2002, using a case 2.630´ long made from a 300 H&H Magnum case and the load noted above, I shot five 5 shot groups averaging 1.468".
After shooting, the 2.630´ case was 2.626´/2.628´ long, it had blown out and shortened.
The problem was that the 300 H&H cases were tapered, and a 300WM case formed from them and trimmed to just fit in the chamber, shortened after firing. I needed longer cases.
The test with a long case made from a 375 H&H Magnum case
I went to the Internet and asked for samples of 375 H&H Magnum cases, which don¶t have the taper of the 300 H&H. Alston Jennings was kind enough to send some. I formed three of the cases to 300 Winchester Magnum, leaving the necks long.
On March 27, 2002, with one case formed to 300WM 2.642" long and the same load, I shot five 5 shot groups averaging 1.438"
After these 25 shots the case length was 2.646´.
The test with the long 375 H&H Magnum case trimmed short
I then trimmed the case to 2.605´ and shot five 5 shot groups averaging 1.036", same load as above.
After these 25 shots the case was 2.608´ long vs. 2.605´ before the shooting.
Lengths of 300 WM cases
"Book" case length 2.620´
"Book" trim to 2.610´
My rifle chamber length: 2.648"
Formed from 300 H&H, case length: 2.630" after firing, 2.626"/2.628"
Formed from 375 H&H, case length: 2.642" after firing, 2.648"
Formed from 375 H&H, case length: 2.605" after firing, 2.608"
Table of group sizes fired with 300 WM cases of different lengths, inches.
Date 13-Mar-02 21-Mar-02 27-Mar-02 27-Mar-02 Case Length 2.605" 2.630" 2.642" 2.605"
First 1.378 1.117 0.978 0.880 Second 0.821 1.073 1.497 1.627 Third 1.111 2.224 1.099 1.106 Fourth 0.986 1.653 1.399 0.785
All these groups were shot at a pace determined by the time required for reloading the one case. No wind flags were used, the rangemaster stopped the shooting after each 15 minutes of ³hot line´ for target change. The gun was cleaned once at the end of the day.
Comments and Conclusions
I don¶t like to use cases that are close to the maximum possible length. If the case lengthens slightly, then excessively high-pressures will be experienced as the bullet and case neck are jammed into the leade/throat/ball seat..
The average group size for the 20 groups was 1.23´. Six of 20 were under an inch.
Pressure was high enough, bullet hardness was low enough (new wheel weights) and the bullet had an exposed section outside the case about 1/8´ long ready to expand or obturate. I believe that the results are germane to all cast bullet shooting disciplines. There were no called flyers in 100 record shots from the bench. There was one stranger in the third group shot on 3/21/02.
I see no accuracy improvement using longer cases. The hypothesis failed this test.
One test doesn¶t establish the fact, but I have seen no data supporting the hypothesis that longer cases improve accuracy in soft cast bullet shooting. If longer cases do produce better accuracy, I want to know it. I would welcome any other data on either side of the issue.
Since writing the above I have worked with a Savage 12BVSS in 223, forming brass from 222 Magnum cases because the chamber/brass on hand combination resulted in a gap between the end of the case and the end of the chamber. I was not able to detect an improvement in accuracy.
And I've been working with my Martini bench rifle and a M54 Winchester rifle, both in 30/30, both with "long" chambers. Using Buffalo Arms "long" 38/55 brass, I've formed 30/30 brass about right for the chamber.
I was not able to detect an improvement in accuracy with longer cases in either of these guns. I'm still trying.
Jeff Bowles mentioned (on the CBA Forum) that he makes (from 30/06) 308 Win cases that are .0015" from the end of the chamber and that this enhances accuracy.
Frank Marshall, in "Neck Length and Accuracy In Cast Loads", TFS March-April 2005, page 174-9, mentions seeing substantial accuracy improvements when using cases with "long"
necks-not to exceed the chamber case length of course.
Here are some other test results with "long" and short cases:
"The rifle was a Winchester Highwall, a hunting weight (8 1/2 - 9 lb with scope), 22" Bauska bbl and a 6x18 Bushnell Banner.
The loads and groups were as follows:
Sept. 24 '01 - 31141 - 20:1 - 12.5 gr H110 38 - 55 brass 1.25"
30 - 30 brass as above 2.3", 1.65"
Sept. 25, '01 - Lee 311155 - ww +2% - 28 gr Ammomart #44 38 - 55 brass 1.3" Called flyer, 4 in 0.75"
30 - 30 brass as above 1.60"
Oct. 6, '01 - 311403, - 20:1 - 8.3 gr Unique 38 - 55 brass 1.37"
30 - 30 brass as above 2.1", 2.8"
I started out with only 5 38 - 55 cases, so testing was a little skimpy. These cases were trimmed by trial & error to just fit the chamber length. The 30 - 30 cases were trimmed on a lee case trimmer to their standard length. The length difference was visually obvious, but I have no means of measuring it. Three different loads, different powders, different bullets, different days seemed indicative to me that I should buy brass.
It seems to me that similar results were had with my son's rifle, a rolling block with a 4x12
It seems to me that similar results were had with my son's rifle, a rolling block with a 4x12