9mm Luger AR9 PCC bulges in lower half of case

[Kocher]

Started running my new AR nine pistol, caliber carbine, and 9 mm. PCC.

all the components from Aero Precision PCC 9, including a 9 inch barrel.
all aero precision EPC kit including:
EPC 7.7 oz Buffer Kit includes:
EPC Buffer
308 Carbine Buffer Spring
Enhanced Carbine Buffer Tube


The parts that are not are:

spikes tactical lower (cut for Glock mags)

Frontier arms= side, charging upper (I think that was the name of it. Super high-quality fits really tight no wiggle.

nickel plated fail zero bolt.

I ran shooters world clean shot:

4.5 gr Berry 115 grain RN
4gr Berry 124 grain RN

shooters world clean shot= warm weather ran great no issues in the PCC and my MP five.

Cold weather=case bulging, and one of them even exploded, and I have a primer pierce.

shot probably 300 to 400 rounds and this did not happen all the time

it looks to be about 20 rounds or 30 rounds that had issues.

clean shot = paradoxical effect ?
warm weather=lower pressures
colder weather =higher

I have ran CFE pistol with 124 grain and 134 gr= no issues
Of course the MP five was perfect the entire time no bulging cases all looked fantastic, including the lowest of recoil, between the PCC, I own.
bulging cases = all different brands.

I will also add I have had issues with shooters world powder before in pistol. Probably due to not working up the load.


Clean Shot= very sensitive to cold temperatures and pressure spikes??? I shouldn’t spread rumors because I have no data stating that.

Some cases were longer than the others and I over crimped them?

Mp5 = not as affected, as if the pressures would be still up, not able to eject the case?

I will now start to put brands in different piles as to try and keep the lengths, the same when loading the batches so that we don’t have different crimp pressures on these bullets.

 

[RegionRat]

One case bulge like that would have had me at hello...

Play it safe.

With your eyes and fingers, you don't get warranty replacements on your parts or your parent's labor. Good Luck.

 

[Kocher]

Unfortunately I didn’t know there was an issue until case separation… that is the risk with these pcc/blowback designs.. I really don’t know what happened for sure, but from what someone else posted on a 9 mm handgun he had similar issues when it was over pressured?
I may pick up one of those rolling lock, buffer tube kits… it is supposed to transform a ar9 to work similar to mp5 roller lock… will see..

 

[RegionRat]

I haven't tried the buffer trick, but I do have the CMMG design for their radial delayed blowback and like it very much.

 

[308pirate]

I will also add I have had issues In particular, ultimate pistol for a load for 45 ACP, I pulled the bullets and measured the grains = they were within the amount specified in their reloading manual although it was .3 grains short of max 45 ACP…
These 45 ACP rounds were literally transformed into a 45 super velocity!!
It was quite scary!
I think it was 230 grain traveling at 1500FPS!!!

Something doesn't add up in this story

 

[alamo5000]

First off those pics look scary. Really scary. If I had just one of those I would stop shooting the whole lot.

I think there are several other things you need to look at and/or tell us about.

How do you resize your brass? What die? What press?
Have you performed a 'plunk test' using that exact upper with any of the reloads?
How carefully did you examine the brass after sizing?

Some of those brass look like they suffered from Glock Bulge®, more than likely before you ever got them. This is a high possibility if it's once fired range brass.

I wouldn't instantly point the finger at the powder as it could easily be a sizing issue. I had a pistol before that had an EXTREMELY TIGHT chamber. My loads that ran in everything else flawlessly would not at all even feed into that pistol. If that new barrel of yours has a super tight chamber it could be something to track down.

To me though, at least some of those cases look like it was caused at least partially during resizing. IE Glock Bulge® then having a tight/semi tight chamber will compound the problem. Even if they are 'resized' most dies do not remove The Bulge® at the base of Glock fired brass so it could cause a feeding issue.

Not saying this definitively but rather giving more options of something to examine before laying absolute blame somewhere else.

 

[308pirate]

Not a “professional” reloader yet never had any issues with any other brand of powder…yet the 2-times I have goofy velocities and cases expanding it is with Sw powders
could have been my fault …I would hope that it was all me… when I loaded the same stuff for the 9mm cz shadow 2 although i didn’t chrono it…seemed okay…. so most likely I did something… If it isn’t scientific it is all bullshit?

It seems you don't chrono anything. If you did, and followed common sense practices like starting at the bottom with a new powder, you probably would have avoided 45 ACP ammo generating unsafe velocities.

And stop with the "I'm not a professional" bullshit. None of us are.

 

[MarinePMI]

My limited knowledge of 9mm AR uppers, and blow back actions, tells me two things (or at least what I can make out from your post, which seems to be a bit disjointed):

1. Your load is too hot.

2. And because either the load is too hot, or your buffer is too light, the bolt is beginning extraction before pressures have begun to lower. So, your case is extracting when pressures are still high enough to balloon the casing just ahead of the rim.

This same exact thing happened when folks were trying to run 17HMR in a 10/22M with just a barrel change. And for the exact same reason. A lot of early gen glocks had this same issue (though not as severe). Hence the term "Glock bulge" for 9mm brass fired from a glock.

Were it me, I'd look at the buffer spring and buffer. If those loads are within published velocities/pressures, then it's most certainly something to due with the timing of the gun.

JMTCW...

 

[alamo5000]

...early gen glocks had this same issue (though not as severe). Hence the term "Glock bulge" for 9mm brass fired from a glock.

I don't own, nor have I ever owned a Glock, but my understanding was that the bulge created from Glock pistols was/is an intentional design thing. Slightly loose tolerances and all that jive and an unsupported chamber was part of the plan. I could be totally wrong though. I simply do not know the answer.

That said, supposedly they included that in the design to aid in reliability with just about any ammo you can find.

In that context 'the bulge' is not a bad thing at all. It however is not ideal for reloading but for the main purpose of the handgun it's a good thing, especially for those who cannot pick and choose which ammo they run.

 

[MarshallDodge]

I would run some factory 124 grain 9mm loads in it to see how that goes, just to rule out ammo as the issue.

 

[45-90]

The components and build parts seem normal. The load doesn't appear to be excessive pressure.

It looks like it's firing out of battery.

The huge bulge is all around the case, on some. Clean chamber, go gauge it with a go gauge... and check the bulged cases for excess length. Long cases stick out of the chamber farther so ya loose the heavy portion of brass support.
I use bulk 9mm brass and it varies in lenght from many countries around the world.
I run +P+ in my 9mm ARs as standard loads...I do not use anything but jacketed bullets.
They are cheap and do not build up lead, in the chamber and lead shavings pieces in the chamber or thin plating flaking off... causing such problems.

 

[Kocher]

Many years ago when I shot in police explorers pistol competition, I purchased my reloading equipment, bullets, etc. from a company that reloaded all of the ammunition for the Minneapolis police.
Minneapolis police had just transition to Glock 9 mm

When I spoke to the owner 30 + years ago… (this company had skin in the game because it was his reloads that were exploding in the Glocks)

The reason he told me: was the case was not supported very well. (barrel had very little support on the bottom half of the case (causing a half moon mark on the one side of the case, and some completely around)
Glock changed the chamber area as to support the case, and that ended the bulge issue on the glocks. Or at least the exploding issue when using reloads.

Minneapolis police did a no reload policy and that ended any issue. They still to this day only use factory ammo.
Which is interesting because if you look at the history, they always use reload ammo while practicing, especially with the revolvers, but not anymore those were different times them

I pick up many one shot cases at the gun range and there’s a lot of Glocks being shot. None of them are bulged.

 

[Kocher]

wow, gentlemen, appreciate all the candid response. All that information is important to know for any semi auto gun.

Thinking back on that day I remember even my German roller lock delay sub gun was throwing cases 5 to 6 feet to my 4-5 o’clock!
2nd time shooting both carbines, the first time was an indoor range.

I broke the cardinal rule of working up loads slow before throwing down 1,000 reloads on the Dillan 650 XL! Even if I don’t think that was the cause I still have to start doing things differently.

i’m taking these important lessons that I have to let sink in:

1-always start low and work up on the powder charges when shooting a new gun

2-if possible shoot factory loads to see what the gun does with the normal charge and what it looks like it feels like so that you know when it’s not

 

[Kocher]

It seems you don't chrono anything. If you did, and followed common sense practices like starting at the bottom with a new powder, you probably would have avoided 45 ACP ammo generating unsafe velocities.

And stop with the "I'm not a professional" bullshit. None of us are.

Well, I do try and Krono when I can but I don’t have one of those fancy Garmin or lab radars.
That means I’ve got one of those dual light beauties that’s got two sailboat sails sitting right over the top of it.

Attempting to put that up in 30 mile an hour winds in 30° weather( which we constantly have here in the Midwest.)

Even if you manage to get it buttoned up on a tripod and mounted , those sailboat plastic thingies go flying off the rods.
If you’re blast from the barrel, doesn’t blow them off the wind will!

If you want to try and bring that plug-in laser light shit show @ an indoor range? I’d love to see how far a person would get while attempting to set up one of the optical, 80’s porno-chrono monstrosities, before getting escorted out of the gun range.

if you hear the frustration, then you are correct.

If I’ve got a powder that’s so sensitive as to .3 grains and it’s overcharge .3 less it is just enough to make it work tells me it’s the wrong powder and run away from it. Especially when it says that it’s within range of a normal 9 mm not +p.

chamber seems plenty loose. Definitely not a tight chamber when comparing to semi pistol.

I Have 1,000 rounds of SW ultimate pistol 5.2 grn under 124grn platted bullets to shoot
When it gets warmer out as it’s about 30° and snowing now.

Max is 5.6grn. …
I will chrono it and see.
I will report back I plan to shot 500rounds of it in both the German rolkerlock and the pcc… don’t have any left to try to “work up”. So will have to be careful and look at the data….

 

[Kocher]

When I look at reloading rifles, I can (count on the accuracy of the load data.bullet and powder, and I know when I’m getting close to the max, without ever bringing it to the range and firing shots unless it’s a wildcat round . I’ve never had a rifle whether it’s 6.5 Creedmoor, 6 Creedmoor 5.56 or 17 Remington be it 1 or a .5 grain off the maximum and it was way over pressure.
is this so different with pistols?

 

[spife7980]

When I look at reloading rifles, I can (count on the accuracy of the load data.bullet and powder, and I know when I’m getting close to the max, without ever bringing it to the range and firing shots unless it’s a wildcat round . I’ve never had a rifle whether it’s 6.5 Creedmoor, 6 Creedmoor 5.56 or 17 Remington be it 1 or a .5 grain off the maximum and it was way over pressure.
is this so different with pistols?

Volume, bottle neck rifle cases have much more volume in relation to the bullet than pistols do. Age why oal is a more important driving pressure in pistols than in rifles as well.

 

[308pirate]

Well, I do try and Krono when I can but I don’t have one of those fancy Garmin or lab radars.
That means I’ve got one of those dual light beauties that’s got two sailboat sails sitting right over the top of it.

Attempting to put that up in 30 mile an hour winds in 30° weather( which we constantly have here in the Midwest.)

Even if you manage to get it buttoned up on a tripod and mounted , those sailboat plastic thingies go flying off the rods.
If you’re blast from the barrel, doesn’t blow them off the wind will!

If you want to try and bring that plug-in laser light shit show @ an indoor range? I’d love to see how far a person would get while attempting to set up one of the optical, 80’s porno-chrono monstrosities, before getting escorted out of the gun range.

if you hear the frustration, then you are correct.

If I’ve got a powder that’s so sensitive as to .3 grains and it’s overcharge .3 less it is just enough to make it work tells me it’s the wrong powder and run away from it. Especially when it says that it’s within range of a normal 9 mm not +p.

chamber seems plenty loose. Definitely not a tight chamber when comparing to semi pistol.

I Have 1,000 rounds of SW ultimate pistol 5.2 grn under 124grn platted bullets to shoot
When it gets warmer out as it’s about 30° and snowing now.

Max is 5.6grn. …
I will chrono it and see.
I will report back I plan to shot 500rounds of it in both the German rolkerlock and the pcc… don’t have any left to try to “work up”. So will have to be careful and look at the data….

Spare me the excuses. I live in the midwest, I have a cheap chrono just like yours, but somehow I manage to make safe ammunition.

I think you need to stop reloading before you hurt someone else (IDGAF if you just hurt yourself) and just buy your ammo from the store.

 

[FuhQ]

Something doesn't add up in this story

I wonder if he recalibrates his scale before each time he loads… The only time I ever had an overcharge issue like that was about 10 years ago, and I was in a hurry and forgot to recalibrate the scale before loading, and almost blew up my new custom .25-06 AI. Now I recalibrate them every time before loading…Never had that happen again.