What caused this

[bigedp51]

This photo was posted in another forum, would using too slow a powder and high port pressure cause the case to balloon on extraction. And if it were a out of battery firing wouldn't the base of the case have ruptured? I have never seen anything like this before and have been reloading for over 47 years.



Can you see me now?

[gaijin]

I see no photo and need additional info; what firearm used, bullet, case, powder and charge?

[Ned Christiansen]

Gonna guess it's a bulged .223.... they "look" like it must have been out of battery when it bulged but really they're just bulging into normally-occurring, available space, that being the chamfer at the back of the chamber and the chamfer at the mouth of the bolt face recess. If I'm right, what you have is a round that was over pressure for some reason and the gun was within half a PSI of getting blown up.

[markm]

With no pic, I'm also guessing .223. I've only seen bulging on my Wylde chamber with hotter loads of .223.

[thopkins22]

I can’t see the photo on my iPad, but things have to be really out of spec to fire out of battery. Like really out of spec to the point that even when all the evidence points to that happening I’d still be skeptical and look for something else that could have happened...likely what Ned suggested.

[Ned Christiansen]

Hm. Look how short the necks are. The dimension from the base to the top of the bulge is longer than expected, longer than the distance from the bolt face to the end of the chemfer lead-in to the chamber (unless it's way, way deep. Those short necks are telling us something, just not sure what, yet.....

Has this gun been fired before successfully, has anything recently been changed (bolt, barrel), any chance this is .222 ammo?

Maybe the necks are getting short because the brass to make that bulge hadda come from somewhere. In which case.... looking at that lead-in chamfer again.

[Kansaswoodguy]

Incipient head separation maybe or to light of buffer idk that’s a new one on me

[P2000]

Like others say, also gonna guess bulged/over pressuer .223, maybe with a soft or thin brass at the head.

Even with a slow powder in a carbine gassed 16", I can't see unlocking happening prior to the bullet leaving the barrel, and if it did, the head would separate and blow out and not just bulge. In other words, the bulge is evidence that the base was supported during the pressure event.

[1_click_off]

Wonder if there is a broken neck in the chamber keeping it just far enough in battery it fires, then the forces slide it back enough for the bulge.

[mack7.62]

^^^ check this. Possible bolt not fully locking and unlocking too soon. Details of rifle/load might help.