I have reloaded for 20+ years. Am a big brass scrounger and have am sure I have picked up some brass that has run through Glocks with unsupported chambers. Never have I seen a full bulge ring around a case.

This brings me to the picture attached. My brother shot (3) 10mm guns at range the other day. He went through a couple of hundred rounds and we were able to pickup about 150 of them. Several of them had a VERY large bulge at the base just above the rim. Is that from an unsupported chamber in one of his guns? He was shooting an XD, S&W and an AR pistol in that caliber. Was able to resize one of the brass with quite a lot of difficulty. Unsized brass with bulge is .965, the sized brass brought it back to .982, just .005 away from size to length, per Hogdon. No primer crushing or any signs of overpressure on any of the bulged cases.

Should I reload or discard these cases? Is this what an unsupported chamber does?

Attached Images

10mm.jpg (120.1 KB, 146 views)

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Tim
Um, hmm, yes it is so

Most of us would toss them but there are a few of us that
would size them and if they plunk, in your chamber, before priming,
give them one more send off.

I have shot and reloaded 9s, 40s and .45s for and from Glocks for years and never seen a case that looked like that. I would pitch them.

Toss them! They will let go completely next time. I have had three Delta Elites in my life, and ALL of them did this. I no longer have them. My Tanfoglios, Rock Islands Kimbers do not do this, but all have ramped barrels, not beveled chambers.

Since you listed that a AR pistol was used, it may be where the cases were fired. A blowback type of AR can produce cases like this if buffer weight and buffer spring is not matched to cartridge/load. It be a sign opening well before peak chamber pressure and bullet exiting barrel.
It would be advisable to not reuse case.

This may be it, the gun is a CMMG Banshee and my brother is seeing that early unlock may be an issue on this on other forums. He is calling CMMG tomorrow. He did say it came with 2 buffers. Using Rainer 180 grain plated with 9.2 gr Alliant Power pistol. Alliant shows 9.3 does 1,295 FPS. Would have thought CMMG would have the standard buffer for 180 gr in the gun?

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Tim
Um, hmm, yes it is so

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If it's a true AR pistol that's the one doing the damage.

My 10Auto CMMG Banshee & my son's 10Auto Kriss Vector will bulge hot handloads. Factory loads are generally not hot enough to bulge.

It's not the buffer spring that causes the problem, it's the design of the bolt face which is of typical rifle design. (I've used a buffer heavier than CMMG's H3 5.5oz buffer & it doesn't change a thing.)

Rifle cartridges have very thick brass above the web & can handle the lack of support.

10mm brass is designed for pistols which overwhelmingly have chamber support. Without that support 10mm brass is too thin & will bulge if pushed too hard.

Normal brass expands to .430-.433", without a bulge.

If it expands .434-.436" (just above the web) I'll resize them & only use them for moderate loads in fully supported chambers only.

If they're over .436" they go in the trash. (Bulging stretches & thins the brass, weakening it.)

Don't waste your time with CMMG. They know about it & won't help.

9x19 AR pistols will do the same thing but you have to go into +P+ territory to bulge them because 9mm is naturally thicker than normal pistol brass above the web.

Also, don't waste your time measuring un-sized brass. The reading is meaningless since the case is not straight, it's bowed out regardless if it's bulged or not

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Waiting for the break of day

I've shot almost 1000 rounds thru mine, overwhelmingly handloads & I've tested hundreds of combinations to find the point of no return with the bullets & powder I like. I mainly use 165gr bullets.

I chrono'd & tested this in my 8" Banshee:
180gr FMJ-FP:
P-P @ 8.4gr= 1236mv, 8/ea, 100% normal/no bulging

What brand brass you use can make a difference too, of course.

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Waiting for the break of day

Thanks BLUEDOT37! Will try that combination for next run. Which buffer are you using?

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Tim
Um, hmm, yes it is so

The "unsupported case" problem you mention usually produces a bulge on one side of the brass. Shaped sort of like the end of the ramp. I've seen it called the "Glock Smile".

Your issue is different and I've learned something new today.

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Just Say No - To Social Media

I started with the CMMG H3 buffer @ 5.50 oz, then slowly built up the weight in an Optimus buffer where you can try different combinations of weights.

Ultimately I ran the Optimus with (4) tungsten weights in it @ 6.80 oz, the heaviest weight you can get in a buffer, as far as I know.

Don't really see where the extra weight did anything for the bulging but it might of helped a little keeping the ejection pattern more rearward on the hot loads.

FWIW, I did change from using the Militec-1 oil lube on the Banshee's BCG & started using TW25B grease instead.

Also, in my testing, I found that S&B's brass was slightly better at reducing bulging, up to a point, than Starline & several other major brands.

But again, the AR's bolt face design doesn't allow 360 degree support (at the web) which the 10mm pistol brass can only handle to a point.

I mentioned above that normal case expansion (in the Banshee) was .430-.433", the best I observed. The same hot loads shot in my M1006 measured .428-.429".

The fastest 165gr loads I tested in the Banshee gave 1542mv & 871/me with 13.5gr/AA#7 (above published max), but the brass was trash. No problems when shot in my M1006 (1433mv & 752/me) though.

12.5gr/AA#7 was a compromise at 1461/mv & 781/me with some bulging. 12.0grs (about published max) gave no bulging & ran 1406/mv & 723/me.

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Waiting for the break of day