Lets get an educational discussion going on the problem of case separation   ie what causes it and what can we do to avoid it. 

This was triggered by the ingoing discussion of the 32-20 shuttleworth heavy bullet but I thought it deserved a broader discussion that would be easier to find in the archives.  I seem to recall that is can be a problem with other small capacity cases.

My limited understanding is that it is caused by migration forward of the case material which leaves the brass thin and weak immediately ahead of the web.

I have only experienced it with 2 rifles both bottleneck cartridges.  one was a old .303 SMLE and they had notoriously generous chambers and reusing the brass was never a consideration in their design. 
The other was in my BLR lever gun rebarreled and rechambered for the 6.5Redding/260Rem.  I was using various milsurp 308 brass and had a few head separations and real sticky cases--shooting jacketed bullets of course. In this case careful neck turning (and switching to factoryammo/commercial brass)  solved it.  I think the too-fat neck/too-tight chamber raised pressure and pushed brass forward----but thats a WAG on my part

My shooting Buddy in PA use's the CPA 32-20 breech seated 200+ grsin bullet in CBA match's, he fires his cases some times two match's a month (200+rounds) plus practice (# rounds unknown), he called me last spring when he started with the CPA 32-20 complained that he had a few cases separate on him, I told him quit being so cheap and buy a couple hundred new case's after talking to him and try the AA4100 that John L. had recommended to me for my 32 Ideal, since he started using the new cases and the AA4100 no case separation's and since he changed both items at the same time hard to tell what made the difference, but I feel those couple boxes of fired in a revolver old Remington 32-20 cases were the problem.
Mike

PS: I have had a few case separations in my 50+ years of reloading most of them using old foreign military cases in 303 British Enfields most were complete separations using jacketed bullets and in well used 94 Winchesters 30-30's with many times reloaded cases usually partial separations & close to max cast bullet loads.

the interior dynamics of a cartridge undergoing combustion must be pretty exotic in those few nano-seconds 

  Just got to wondering------ is any possibility of brass erosion or perhaps being burned away after many firings. 
If so maybe different powders burn hotter and cause more brass erosion than others.

I wonder if a case that had been fired xx number of times has actually lost any weight of brass?  Might be interesting to weigh a new un-fired case and compare it to a clean but well-seasoned veteran case

This is a very interesting thread to me and as I mentioned on another thread in regards to the head separation experienced with the 32-20 cases blown out to .321 I failed to mention the numerous brand new cases that had to be discarded and were at the raged edge of separation some after just one firing. Does anyone feel the process of blowing out these cases is directly related to the start of the separations and that cold forming the brass would be a better approach. The other issue not mentioned is after one firing the webs expand to the point of extremely hard extraction and requires the cases to be re-sized on a somewhat regular basis. 

40 Rod I tend to think you are onto something in regards to annealing and its importance with the use of some of these smaller cases. 

Mike T it would be interesting if you could talk  your friend to change back to the other powder he was using on an experimental basis to see if the separations return. Out my way the powder definitely made the difference as the cases remained the same. 

J.Louis

frnkeore wrote on Nov 13^th, 2011 at 1:15pm:


I have to agree with you Frank, Earl says he uses 1/8" thick floral foam now to keep the powder from getting free, he was using cork with the original old cases when he had the separations. (did the cork cause the problems, I do not believe so as the old Rem brass he used had been fired in my S&W 1905 revolver more than a couple times, and I know that the heavier loads do stretch in that revolver as I had separations!)
I Know that all the CPA rifles I've dealt with breech up tight and IMHO do not have much movement if any at all when fired.
Mike

Mike here are some stats with the 32-20 and 12.5 gr AA 4100 - av mv 1543 fps - ext spread 10 fps - std dev 2.92.

Those fellows out your way using 12.8 and 12.9grs must be achieving some remarkable velocity levels not knowing how the difference in elev, humidity, temp. etc. comes into play. It would be interesting to know what their pressure levels might be and how it might be related to their separations. Some amazing performance levels coming out of that short cartridge on your end. 

J.Louis

John,
If the case heads are expanding, it can only be that the brass is to soft for the pressures envolved.

I talked to Starline about 7-8 years ago and they told me that for cartridges that develop higher pressures, they "hit" the heads a greater number of times to work harden them for the higher pressure.

Maybe some older brass marked HV would work better in the 32/20 loadings but, finding them might not be easy.

Frank

When cases are made they are annealed more that once throughout the manufacture process. The engineers have worked out temp, time, quench, to get what they want. When we anneal we heat um up till they glow and then quench them. This works well for long cases but with short pistol length cases I think it is easier to get the anneal too far down the case. Eventually the thickness of the web modifies the process. When the cases go under pressure the softer brass flow while the harder brass resists. over time maybe as short as a few shots, a thin spot develops. 

40 Rod