Broken case....... lessons learned

[Mozella]

Tell me how you get case head separation if your brass is properly sized to the headspace of the weapon?

For the same reason so many companies sell case trimmers. As you repeatedly fire and then resize cartridge cases, the brass gradually flows from the body up toward the neck. Since the base (also called the "head"....... go figure) is both thick and hard, the mid case region is most effected.

Resizing the brass does not reverse this brass flow and from time to time the neck needs trimming. That, of course, is why they sell trimmers. Eventually, after many firings, the case body thins to the point that it will separate even when using rather mild charge weights. This is common enough that various companies sell devices to detect and measure this kind of case thinning. I own one such device, but I rarely use it unless a case shows some kind of external hint of excessive thinning. Old brass, if you clean it carefully, will often show a slight discoloration on the outside and, if you use the proper testing device, you can detect and measure this thinning and reject the brass before it causes a problem.

 

[rogn]

Tight tolerance chambers good brass and minimum sizing will allow brass to live indefinetely. I shot Rem BR brass in a good tight camber,with tight neck and fairly heavy loads. At a bout 100 firings the primer pockets on some cases reprimed easily. They were trimmed only once during this time. The cases were still useable but the barrel was worn out. When you move brass around after every firing, such as needed with conventional chambering and conventional dies(which oversize due to need of chamber tolerances) brass is going to stretch and work and fail. Thats why they make more brass. Survey your fired brass and discard as indicated by stretch marks, need to trim or anything that just doesnt feel right. Youll not likely have a case failure. Ive never had a case head separation in many years of shooting, i have had cracks near the case head in factory ammo. Now that Ive said that Ill probably have one real soon.

 

[209jones]

For myself, I've found that new brass does not always expand to the same base to datum length across 30-50-100 cases, sometimes, even after being shot twice, which made me scratch my head a bit. So, I always set the FLS die after first shot, to only bump the longest ones in the batch about .001+, and then do the same after second shot, and leave it set there, when using an FLS die on a given load. Haven't had separation rings show up since mid 80's on any brass I've had, since I started doing that. Being lazy, for some loads for some guns, I'll usually neck size the first two loads on new brass, saves a lot of work, and I haven't encountered any issues with sticky base areas with that, that I noticed, on my bolts or falling blocks. On some loads, for some guns, I'll neck the first 4-5 loads, FLS, neck the next 4-5. I set the FLS die to bump .001.002 off longest fired for that. I have used mostly mandrels for expanding, discovered that about 35yrs or so ago with cast bullets, way easier on brass, tried some bushing dies, not all that impressed with them so far, they work, add a bit of versatility. Only have one gun that doesn't have a neck die for it, as I'm too cheap to get a custom one made, and haven't explored other cartridges to see if maybe a different 30cal might work on it, the FLS for it was a custom shop die too.