9mm brass bulging, like SCARY bulging!

[halmbarte]

Only thing I can think of is bolt bounce. If the bolt is bouncing off the barrel extension and is already moving back when the round fires it would match your symptoms.

I'd try a heavier buffer and then maybe a different recoil spring.

H

 

[nubus]

My favorite explanation so far...

 

[deadshot2]

Although I like this line of thought, why would repeated "fast" fire cause the blowback action to extract sooner than with "slow" repeated fire?
I also am drawn to think premature extraction is to blame, I think legalizing SBRs in WA would also resolve the issue.
Shorter barrel = less or no pressure upon extraction, just a thought.

A shorter barrel would probably stop this occurance. Slow fire is more in the range of 1 or 2 rounds per SECOND. For FAST fire rates up to 20 rounds per SECOND are possible (like an Uzi or Mac). The longer the barrel the greater the possibility of pressure buildup in the barrel. Yes, both ends are open when the bullet is gone and the case extracted but for how long? Take a look at some video of a sub-gun, paying attention to the gases discharged from the ejection port:

This from a firearm designed to be fired this way and there still is pressure present at the time of extraction.

FWIW, this problem occurs from time to time in semi-auto pistols when they are modified with lighter recoil springs.

 

[halmbarte]

A shorter barrel would probably stop this occurance. Slow fire is more in the range of 1 or 2 rounds per SECOND. For FAST fire rates up to 20 rounds per SECOND are possible (like an Uzi or Mac). The longer the barrel the greater the possibility of pressure buildup in the barrel. Yes, both ends are open when the bullet is gone and the case extracted but for how long? Take a look at some video of a sub-gun, paying attention to the gases discharged from the ejection port:

This from a firearm designed to be fired this way and there still is pressure present at the time of extraction.

FWIW, this problem occurs from time to time in semi-auto pistols when they are modified with lighter recoil springs.

Ok, we're talking about a delayed blowback operated firearm in that video. Of course there is pressure coming out the ejection port as the bolt is never really locked to the barrel extension, it's just slowed down by the rollers. If you were right about the barrel being pressurized there would be a continuous flow of gas out of the muzzle and ejection port while the weapon is cycling.

If it helps, you can think of any blowback operated weapon as being gas piston operated. Just with blowbacks the gas piston is the cartridge case and you only use it once and then toss it overboard.

H

 

[deadshot2]

Ok, we're talking about a delayed blowback operated firearm in that video. Of course there is pressure coming out the ejection port as the bolt is never really locked to the barrel extension, it's just slowed down by the rollers.

And this helps make my point. This is a firearm that was designed to be operated Full Auto. Not the 9mm Carbine version of an AR-15. There's essentially nothing to delay the blowback, other than the weight of the bolt and buffer spring tension.

 

[AMProducts]

Hey there, I do have some input on this, as I had the exact same problem with my oly 9mm upper, which has been very formative in my opinion of olyarms...

What is happening is your gun is firing out of battery, I had this same issue with my 9mm oly upper, however the genesis of your problem is different than mine. I was having rounds that would simply not chamber all the way, and the gun would fire anyways, causing the gun to fire out of battery, typically blowing the magazine out of the well, sometimes blowing the guts of the magazine out through the bottom of the magazine.

However the problem you are having, is somewhat related, your gun is firing out of battery, much like mine does, however yours is doing it because of the slide fire stock. Your gun stock is resetting faster than the bolt returns, this is due to the 9mm bolt being heavier, as it is a simple blowback operation, not a gas-operated rotating bolt like the AR-15/M-16 series normally is. So what is happening is you are pulling the trigger before the bolt is fully closed, and because oly guns will fire out of battery, your gun fires before the bolt reaches full closure.

The only reason why there havn't been any reports (that I'm aware of) of the slide-fire stock blowing up AR's is that they very gracefully handle the hammer falling before the gun is closed because the firing pin does not reach the primer until the bolt is fully closed. Were it not illegal, dangerous, and a really really stupid idea this would be the same as operating your AR without a disconnector. For the most part, the same thing applies to bumpfire devices like this, even if it is legal, it's still dangerous, and a really really stupid idea. I know in the past some of the bumpfire devices did cause explosions and other catastrophic failures of firearms, it still evades me why anyone would want one. Learn to use your trigger finger, yea maybe you won't be able to fire as fast, but you will at least be on the target.

If you want a real machinegun, get organized, and motivate your elected representatives to repeal the hughes amendment to FOPA.

 

[deadshot2]

it still evades me why anyone would want one.

Let me help you understand. There are a couple of reasons. There's the "coolness" factor. Also the need to "impress your friends". It's something that most people outgrow but some never will.

Put it in the category of "here, hold my beer and watch this".

 

[nubus]

As much as I agree with AMProducts, this is as close as I can own without moving to Oregon.
This is by no means a direct replacement, but it is still lots of fun to shoot!

 

[AMProducts]

Let me help you understand. There are a couple of reasons. There's the "coolness" factor. Also the need to "impress your friends". It's something that most people outgrow but some never will.

Put it in the category of "here, hold my beer and watch this".

I was speaking mostly to the history of guns blowing up when fired in this fashion. Yea, I'm all about full-auto whenever I can get someone else to pay the bills for it.

Nubus,

Since you're already in the biz of selling gun stuff, get your type 07 and get your 02 SOT, yea, you're looking at about $550/yr but if you're already maintaining a sales-FFL the SOT is the only additional cost. That extra FFL lets you get all the rock and roll you want. The lightning link and many other real "full auto" devices are out there that you can make with a rock and some metal if you are really determined. While these things are legal, like I said, they are a bad idea and a poor substitute for full auto.

 

[MarkAd]

Funny thing. last week I saw the same case bulge from thing from a glock 9MM.

 

[deadshot2]

Funny thing. last week I saw the same case bulge from thing from a glock 9MM.

Usually the "bulge" from a Glock is all on one side. More of a "beer belly" rather than "muffin top".

 

[mcathcart]

did you figure it out?
my noob thought was suthin like this going on, but I dunno

the image not the text

 

[nubus]

The gun will be heading to Olympic Arms this week.
Turns out there are two bolt styles, the later revision should not be doing this.
The early models had too much material relieved out of the carrier allowing the out of battery event.
At this point we think this is the issue anyway, not to say the rate of fire didn't cause it!

 

[AMProducts]

well that's some good news, I should give them a call and see if they will replace my bolt next time I'm up there... this whole out of battery issue has been enough to scare me off really shooting my 9mm since I got it.

 

[nubus]

If you're not local, you should be able to ship just the bolt to them.
But if the whole Oly thing really bothers you just send me your gun.

 

[olydemon]

Or send it to me, I drive by Oly every day on the way to work. I can just drop it off and get it fixed in person...

 

[nubus]

So I was thinking about making this new case into a wildcat cartridge. I'm gonna call it 9mm muffin top! Or muffin top 9.

 

[deadshot2]

So I was thinking about making this new case into a wildcat cartridge. I'm gonna call it 9mm muffin top! Or muffin top 9.

Or just call it a 9/45. The "rib" will keep it centered in the chamber of a 45. Kind of like a Sabot Round-----minus the sabot.

 

[Gunner3456]

Call it the omni-shot. "Will fit any caliber of center fire handgun if you have a rubber mallet."

 

[AMProducts]

I remember an occasion a few years ago, a bunch of us had gone out to the desert, and one of the guys brought along his father. Well, we went out shooting and were busy blasting away at a large field of lemons, apples, and assorted fruit when the report came down that someone's gun wasn't working. I went to investigate, the problem was the gun would fire, but the cartridges wouldn't extract. It was the father's very nice 1911 pistol chambered in .45ACP. Well, I took a look at it determining it wasn't a lubrication issue, got a stick and popped the casing out, at which point the problem became rather obvious... it was a .40S&W casing. Apparently he forgot to bring ammo, and was going to share ammo with his son, who shoots .40 and only .40. I made this known to him, and was polite enough to both give him some .45 ammo, and not mention it to everyone in the group.