What would cause case separation?

[tonyfac]

.308 at the range today, i had a few case separations. never had this happen before.
Setup: FAL, re-barreled it about 2 weeks ago with a g1 barrel. Re head spaced it with foster go no-go gauges. took it out today to adjust the gas setting. gas was tuned about half way and it started doing this. lowered the gas pressure and it would not cycle. raised it and had the separations. went 2 notches higher and the rifle ran great, no separations, cycled properly, but a little more recoil than i had before. AMMO: these are not reloads, they are surplus ammo. i have shot about half of the ammo with the other barrel, never a problem. i attached picts to see what i mean about separation. the little ring part actually stuck in the barrel and the rest of the case ejected and the next bullet threaded the ring but the bolt would not close.

[Rundownfid]

Wow, I'll just get some popcorn and wait for answer form some savant on this one. Perhaps the throat is tight and the bullet is binding in the neck. However I don't see how that is helped with more gas, that would seem to exacerbate the problem? This is an excellent question and, "tis a puzzlement".

[Flash]

C'mon. Give us one more clue . . . what ammo is this??

Flash

Can't see for sure, but it looks like there might be a bit of marks in the chamber, the neck area, particularly, that won't let the brass release properly.

[Franchi20/28]

The second picture looks like the crimp is still on the remaining ring. The brass didn't expand to let go of the bullet when the round was fired.

Could it be possible that the new barrel was wasn't 'finish reamed'? That's not the right term, but it's not coming to me right now. Some barrels are only "rough" chambered and need to be "finish reamed" for proper headspace by the gunsmith that installs the barrel.

Doug

[cephas]

Whats the primer side of the case look like? Any funky signs there?

[spblademaker]

The crimp does have me interested. That would be where I would start my investigation! As stated above, pics of the bases would be good.

[tonyfac]

these were part of german 200 round battle pack i bought 2 of them at a show. i have shot these in my other fal and cetme and this fal with no problems until i switched barrels. i checked and rechecked the head space and the chamber. nothing obvious, this morning i took a bore light and a magnifying glass and could see nothing out of the ordinary. the barrel came off another rifle that was in good working condition. last night i reloaded 50 rounds with usa brass and if i get a chance today, i will run up to the range and give it a test. i have attached 2 pics or the base of the shells.

[spblademaker]

Primers look fine. Can't wait to hear about the reloads. Pull the bullet on a few of the German rounds and do a case length measurement on them. Your head-spacing could be fine, but if the case length is too long it may not allow the crimp to open the way it should.

[cdi]

Cases normally fail at the other end-
I have shot some of that surplus DAG ammo, and it seems to be pretty good stuff.

I am thinking the case necks are brittle on the lot you have and there is something a little funny going on in that chamber.

Do you have pics of cases that did not separate? It would be interesting to measure them and compare with the unfired ammo.

You need a bore scope to look down into the chamber- I have one here and if you bring it down we'll take a look at it.

I have a few FAL rifles here at the shop that I assembled. I have not seen case failures like that before and as a point of interest, I would like to find out the cause.

[PA Rifleman]

Photos of the unfired ammo, particularly a closeup of the neck area would help. I had a neck cracking issue years ago that turned out to be an ammunition issue. Inspecting unfired rounds revealed the problem.

In your case, I'd look very carefully at the neck area in the chamber, maybe handfeed a finishing reamer in it. For reasons yet unknown, it's taking less force to shear off the end of the cartridge than expand out into the chamber wall.

I don't think a headspace gauge will detect a neck dimensional issue, I recall 7.62x51 headspace uses the shoulder cone for reference, not the neck.