I am using a 9mm PCC (blowback design) with 16" barrel, so hand guns might be different. I don’t normally pickup my 9mm brass, but I did see one of mine the other day and put it in my bag. When I got home, I noticed the case had a slight bulge about a third of the way from the base . 0.395" dia bulge, 0.388" dia above and below bulge.
I have been chronographing (velocity) some ammo, and this AAC is pretty close to the Hornady 124grain XTP +P American Gunner hollow point ammo, but save $$$.
8.4oz buffer, 14.6oz bolt, 23oz total mass
Standard AR-15 buffer spring.
After that day, I added another tungsten to the buffer. So it is now 9.2 oz.
The next time I shoot, I will try to recover most brass to see if any show a bulge. This is all slow shooting, at least 30 seconds between shots.
I was at the range this morning with my 9mm PCC 16" and gathered more data/samples. The only differences were I added 1 tungsten weight to the buffer, so now 9.2oz vs 8.4oz. And the air was hotter, 90 deg F instead of 78 deg F.
I shot 10 rounds of Winchester 124gr FMJ and no cases showed any bulge. The largest dia I measured was 0.389"
I shot 5 rounds of the AAC 124gr XTP and caught all cases. This was a little worse than the one I noticed a few weeks ago.
0.397" dia bulge
0.398" dia bulge
0.398" dia bulge
0.399" dia bulge
0.402" dia bulge
Everything ejected normally and feeds/functions just fine.
What “support” are you looking for? This is the rifle handguard, full floating.
With a chambered round, the bolt is against the cartridge, so I can’t get any picture. I will put a round in the chamber and lock the bolt back for a pic.
Here you go.
The feed cone is large, so it feeds hollow points just fine. A little sticks back, but the bulge section is in the chamber (higher on the case).
It is hard to get a good case wall thickness with just calipers, but from my attempt at measuring the fired brass, the ACC brass wall thickness appears maybe 0.001" thinner than the Winchester I fired today. About 0.013" vs 0.014" thick.
That could be the issue or you might need a tad heavier buffer to keep the brass chambered longer. Is there any evidence of the chamber being relieved in the section where the bulge is happening?
It is close, but it seems the bulge area is chambered fully.
And as we discussed, maybe my bolt is “blowing back” too quickly for the pressure level of the AAC ammo with the 124gr XTP. The Hornady version of this ammo, 124gr XTP +P, doesn’t bulge in my gun either; just the AAC.
A handgun won’t see this, but a blow back PCC might. Since the standard 9mm Winchester, the Hornady loaded +P XTP cartridge, and the Winchester M1152 don’t bulge in my gun; I wonder if the AAC brass is soft or thinner than the others. My caliper measure of wall thickness is not perfect, but it at least appears thinner.
It is functioning just fine, but I doubt those bulged cases are worth reloading…
After all this, I am satisfied to use this ammo in my rifle.
I was wondering if anybody else noticed a case bulge using this AAC 124gr XTP 9mm ammo in a PCC (not a handgun).
It is possible, but not for sure. It depends if AAC is using the same powder in both loads. From my chronograph testing of the Hornady version and the AAC version (XTP), it seems likely that AAC is using the same or a very similar powder as Hornady +P XTP; since in my 16" they measured 1435 and 1410 fps. But a different powder could make the same 1150 fps in a 4-5" handgun, but not the same velocity and pressure profile in a 16" long PCC barrel.
For example, I have fired Winchester 124gr NATO FMJ listed at 1200 fps, but it only measured 1349 fps in my 16" PCC. And Winchester 124gr SuperX FMJ listed at 1130 fps measured 1338 fps in my 16" PCC.
Do you have a PCC to fire your AAC FMJ and check the ejected cases for a bulge? You don’t need calipers to see or feel the bulge. It is noticable.
