Longevity of .308 cases (link to Jouster thread)


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Sven
April 18, 2003, 11:35 PM
Found this interesting post on Jouster tonight...

http://www.jouster.com/cgi-bin/reload/reload.pl?read=8940


Posted By: SlamFire
Date: Wednesday, 9 April 2003, at 2:19 p.m.

In Response To: BULLET CHOICE FOR M1A AND GARAND (JERRY)

Back in 1999-2000 I tried to determine the useful longevity of lubricated cases in a stock 308 Winchester M1a Super Match. I fired the same cases 23 times in the same M1A without a case head separation. I started with approximately 100 once fired LC66 cases. These cases were all fired in the same rifle. They were fired in 58 round matches and 88 round matches. I kept records of the number of matches the cases were fired in. Since there would always be unfired cartridges at the end of a match, I tried to make sure that next match they were used first. Once the cases were on the ground it was impossible to segregate by exact reload number. So some cases were actually have been loaded more or less than others. All cases were full length sized in my Lee 308 sizing die, a Bonaza sizing die, or my RCBS small base die. The die choice depended on my mood, but the Lee die was used for the majority of reloads. I always removed the RCBS case lube after sizing and before priming. I relubricated the loaded cases by hand before shooting them in highpower matches. Most of the time the cases were coated with Johnson paste wax. Sometimes I used Lee Lube. I tried carnumba formula wax Rally paste car wax. The car wax was not as successful as the thicker film lubricants.

I lost many cases to the range gods. Primer pockets enlarged as the reloads increased. If the pocket did not tightly hold a primer I dumped the case. At the ninth reloading the primers appeared high in the pockets, so I reamed the pockets to a uniform depth. I reamed the pockets again at the 16th reload. There are a lot of scratches on the outside of the cases. I trimmed on a Gracey Trimmer which headspaces on the shoulder. For the first couple of reloads, cases needed to be trimmed almost 0.005-0.01". About the third or fourth reload the case growth decreased significantly. I ended up trimming only .001", if at all, between reloads, when used the Lee Sizing Die. Switching sizing dies has caused case growths to .005". On the next size and trim cycle, case growth is back to .001" or less.

Changing the sizing die seems to cause case length growth. If I changed the sizing die, I ended up trimming more material than if I had not changed dies. The first trim after resizing with a new die is usually in the .005" range. Then, if I size again with that new die, on the next reload, material removal is back to the .001" range. I do not know what is going on. I full length size the case to the minimum headspace(should be 1.630") as measured on a Wilson cartridge gauge. The rifle came with a tag that indicated the headspace was 1.633"

I sectioned cases that developed body seams. I never found any discernable internal evidence of a case ring or case necking. The case loses material each trim, but the location or amount of material loss is not visually detectable. The back one third of the case is dark and roughened, showing evidence of erosion. No case rings were ever felt using the bent paper clip technique on the good cases.

Accuracy is unaffected within the limits of my rifle and this shooter. I fired overall HM scores at our club 100 yard reduced range with this brass, and I have shot HM individual scores during rapid fire at 200 and 300 yards, and occasionally at 500 and 600 yards. I am unconcerned/unconvinced that there is a measurable accuracy loss (or gain).

The last I fired this stuff was during the 2000 rattle battle at Perry. I picked up most of my cases but retired them.

Even though the load is the same, the primers on lubricated cases appear more rounded than when the case is unlubricated. This phenomena also occurs with my AR rifle. Obviously the pressure is not reduced, so maybe I am getting a truer reading of the load pressure within a gas gun.

I believe the best lubricants are thick film types. Such as the heavy paste wax, Lee Sizing Die, Hornady Unique, Imperial Sizing Wax, and RCBS water soluble sizing die case lube. If I sized my cases with Lee or Hornady Unique, I would not remove the case lube. The wax type lubes dry and do not attract as much dirt as do the liquid lubes. Which is why I have used Paste Wax. It works, and is cheap. I apply it with my fingers and polish the rapid fire rounds with a cloth. I found in cold weather that I got bolt overrides when the rounds in the magazine were heavily coated with paste wax. I know of shooters who use RCBS case lube to size and leave the cases wet when they prime, load, and shoot. They report the same extended case life characteristics. I did not conduct an extensive survey of lubricants, and maybe some day I will find something better. One that leaves a non-tacky film, is easy to apply, gives good results, and is dirt cheap.

I always tumbled my cases after a match, and I always use a chamber brush to clean out the chamber of a gas gun after I fire it.

This might be of interest on this topic:

From Army Material Command Pamphlet AMCP 706-260 Engineering Design Handbook, Guns Series Automatic Weapons. Feb 1970

Chapter 8 Lubrication of Machine Guns

8-3 Case Lubricant

Although the gun designer is not directly involved with ammunition design, he is directly concerned with handling, loading, and extracting during firing. A smooth chamber is essential for extraction and a properly lubricated case is a decided asset. The lubricant should be a dry lubricant and should be applied at the factory. Considerable effort has been made to find suitable lubricants for this purpose. Some success has been achieved but continued search is still being advised, especially since two independent facilities are not in total agreement.

The Naval Research Laboratories conducted test of brass and steel cartridge cases coated with films of polytetrafluoroethylene (Teflon). Results were outstanding in meeting required protection and lubrication properties. Laboratory results, later confirmed by firing tests, showed low friction and consequently less wear in gun barrels. Other desirable features include freedom from cartridge malfunction, no chamber deposits, decreased ice adhesion, and less chance of thermal “cook-off”. Teflon can be applied to steel and brass ammunition by mass production methods. Its protective ability permits pre belting and packaging of ammunition since no further handling prior to use necessary. Its supply is abundant and its cost reasonable. Thus the use of Teflon in this capacity seems ideal.

Aberdeen Proving Ground is more reserved in its appraisal of Teflon coating. Whether or not the techniques of applying the coatings were similar, those used at APG were not free of coating defects; a high cull rate existed. When tested with cartridges coated with microcrystalline wax, ceresin wax, and uncoated ammunition; the Teflon-coated wax showed many advantages but was also found wanting in some respects. Teflon and micro-wax had better extraction properties and Teflon left a much cleaner chamber than the others; micro-wax was second best. About 50 percent of the Teflon-coated cases had slight bulges after extraction; other types also were similarly damaged but with no apparent significance attached to a definite choice. For dusted ammunition, the Teflon and micro-wax were far superior to the other two types with Teflon having a slight advantage, although when fired in a comparatively rough chamber, Teflon was outperformed by all. Reiterating, the gun designer, aside from providing smooth sliding surfaces, is almost totally dependent on the physical properties of the lubricant to make his gun perform satisfactorily under all assigned conditions.

The last sentence is a summary of the chapter; not a comment on case lubrication alone. A copy of AMCP 706-260 and other out of print AMCP pamphlets can be ordered from NTIS at 703-605-6000.

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Steve Smith
April 19, 2003, 02:51 AM
I believe it. I have pulled my cases from rotation after 6 loadings, but only due to Perry paranoia. I bet I'd get another 6 out of them. I also leave my light coat of lube on. It is easier with the Dillon and I have found no detrimental results. Call me what you will but I have many thousands of rounds downrange using a system much like "Slamfire" outlined and I've had no safety concerns or malfunctions. I DO clean my chamber very well between most matches just in case. I am using Midway spray on lube right now. I use a Bartlesman (upgrade from a Gracey) and a Giraud trimmer. Also I'm using a Redding S Type bushing die with the bushing that has the neck barely touching the expander on the way out...acting as a sweep more than anything. All the necks from RVOW are inconsistent so I trim when I take them out of the box. I am trimming just a hair short of "minimum" and have noticed a small change after the first firing. After that they stay very consistent and don't need another trim before I toss them.

Fatelvis
April 20, 2003, 02:57 PM
I use LC 90 brass for my match M1A. I pay very close attention to FL sizing, using a case guage, to make sure they`re sized within spec. I use modest loads, (40.5-41 IMR4895 under 168 SMK), and I only get 2-3 loadings, after once fired, before I start getting head seps. Why? Im tempted to size less, but I dont want the risk of firing with the bolt out of battery. I just bought a Redding S-style NK bushing die, and body die, just to help concentricity, will this help? Thanx-

Steve Smith
April 21, 2003, 12:06 AM
I would try to use a Stoney Point headspace gauge on my fired brass and just bump the shoulder back with that S die about .002-.003" total and try it informally. Make sure it son't slamfire (shouldn't) and keep your chamber clean. Oughtta work and increase your case life some.

Fatelvis
April 21, 2003, 11:06 AM
Steve, I have a RCBS headspace guage, (the micrometer screw-down type), will this work ok? Ive taken cases that were fired in that rifle with the gas system off, (so it can conform to the chamber more completely, before being extracted), and the expanded cases were alot longer than my sized ones. Also, they arent very consistant in measurements. I know the headspace is within specs, but maybe close to being a little long. I had a good `smith build the rifle a few years ago, (John Holliger), with a Douglas match barrel, and I doubt he reamed the chamber incorrectly. Any help would be appreciated. Thanx-

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