Thread: 9mm brass bulging, like SCARY bulging!

So went to the range today to try out and possibly sell some Slide-Fires. Hadn't tried the new toy out on the 9mm Oly Glock mag AR yet so why not. I'll have to say the rate of fire was impressive, but upon inspection of some of the brass I was a bit concerned, to say the least. (see pic) Needless to say we stopped the experiment. Now this was using 115gr Winchester white box and the factory supplied buffer. What I can't verify is if the bulging was a result of premature extraction or actually firing out of battery. I would think an out of battery ignition would flat explode the case. But I'm curious to see what any of you think of this. I would say about ten percent of the cases did this out of a single 33rd magazine.

Good Lord what ever you did it's not working. I would assume it is pulling the case out before the pressure has excaped the bore.

My guess would be extracting early. The excess pressure is blowing out the weaker part of the brass above the head of the case.

H

I would ask the guys at Slide Fires. Maybe the setup is intolerant to the SF. I'm interested in one for my AR .223. Have you tried that yet?

that's spot on - all mine look like that too. It's a bit tricky on the resizing die tho - you gotta press really really hard.

OOOOOHHHH I Want one!!!!!

Slide Fire’s

Originally Posted by mikeli

I'm interested in one for my AR .223. Have you tried that yet?

Extensively, and to put it simply, they work well.
And although this thread was not a ploy, we do have them in stock.
It's easier on a 5.56/.223 because the recoil snap is heavier.
It takes a little more finesse on the 9mm.

When bumpfiring my OA GL AR I had the same problem. Mine would fail to feed though.

Gonna try it on a Colt style setup also.

+ 1
had the same thing happn on a few of them

Originally Posted by halmbarte

My guess would be extracting early. The excess pressure is blowing out the weaker part of the brass above the head of the case.

H

This is a situation were the answer is real obvious. The case is being WAAAYYYY overpressured. When the rate of fire increases the pressure in the barrel from the previous round hasn't fully dissapated yet. The next round is chambered, fired, and meets a pressure "wave" that still remains. All this occurs while the fired case is being extracted. In essence, you are using the firearm in a manner that it was not designed for.

If you continue this "impress your friends" method, I would suggest that everyone stand back, you wear a ballistic vest, face shield, and heavy gloves. sooner or later this will progress from the brass developing a bad case of "muffin top" to a rather dangerous Ka-Boom.

Originally Posted by deadshot2

This is a situation were the answer is real obvious. The case is being WAAAYYYY overpressured. When the rate of fire increases the pressure in the barrel from the previous round hasn't fully dissapated yet. The next round is chambered, fired, and meets a pressure "wave" that still remains. All this occurs while the fired case is being extracted. In essence, you are using the firearm in a manner that it was not designed for.

If you continue this "impress your friends" method, I would suggest that everyone stand back, you wear a ballistic vest, face shield, and heavy gloves. sooner or later this will progress from the brass developing a bad case of "muffin top" to a rather dangerous Ka-Boom.

If that is correct, how do full automatics function without this occurring.

FULLY AUTOMATIC WEAPONS are designed by their manufacture NOT to fire above their CYCLIC RATE OF FIRE. I am no expert so I have to ask what the cyclic rate of fire on the weapon in question is?
Here is the definition of cyclic rate of fire:
Cyclic rate

This is the mechanical rate of fire, or how fast the weapon "cycles" (loads, locks, fires, unlocks, ejects). Measurement of the cyclic rate assumes that the weapon is being operated as fast as possible and does not consider operator tasks (magazine changes, aiming, etc). When the trigger is squeezed, the rate at which rounds are fired is the cyclic rate. Typical assault rifles have a cyclic rate of 500–900 RPM. Typical infantry machine guns have rates varying from 600 RPM to 1,200 RPM. M134 Miniguns mounted on helicopters can achieve rates of fire as high as 50 rounds per second (3,000 RPM).

If you make a weapon shoot FASTER than its cyclic rate you are going to have problems. Bulging cases might just be one of those problems.
Mike

Originally Posted by bruzer

FULLY AUTOMATIC WEAPONS are designed by their manufacture NOT to fire above their CYCLIC RATE OF FIRE. I am no expert so I have to ask what the cyclic rate of fire on the weapon in question is?
Here is the definition of cyclic rate of fire:
Cyclic rate

This is the mechanical rate of fire, or how fast the weapon "cycles" (loads, locks, fires, unlocks, ejects). Measurement of the cyclic rate assumes that the weapon is being operated as fast as possible and does not consider operator tasks (magazine changes, aiming, etc). When the trigger is squeezed, the rate at which rounds are fired is the cyclic rate. Typical assault rifles have a cyclic rate of 500–900 RPM. Typical infantry machine guns have rates varying from 600 RPM to 1,200 RPM. M134 Miniguns mounted on helicopters can achieve rates of fire as high as 50 rounds per second (3,000 RPM).

If you make a weapon shoot FASTER than its cyclic rate you are going to have problems. Bulging cases might just be one of those problems.
Mike

The cyclic rate for this design of firearm with 5.56mm ammo is just under 1,000 rounds per minute max.

One solution for this problem might be the use of a different buffer. Something like an Enidine hydraulic buffer could be used to slow the rate of fire to the point that the pressure has diminished sufficient to prevent this bulge.

Originally Posted by deadshot2

This is a situation were the answer is real obvious. The case is being WAAAYYYY overpressured. When the rate of fire increases the pressure in the barrel from the previous round hasn't fully dissapated yet. The next round is chambered, fired, and meets a pressure "wave" that still remains. All this occurs while the fired case is being extracted. In essence, you are using the firearm in a manner that it was not designed for.

If you continue this "impress your friends" method, I would suggest that everyone stand back, you wear a ballistic vest, face shield, and heavy gloves. sooner or later this will progress from the brass developing a bad case of "muffin top" to a rather dangerous Ka-Boom.

Sorry, but you're wrong about the cause of the over pressure. Dead right about taking precautions for a OOB case rupture.

For you to be right the barrel would have to retain pressure after the bullet has left the bore AND after the fired case has been extracted (barrel now has a hole at both ends) fired case ejected, bolt reaches full recoil, strips the next cartridge, feeds the next cartridge, and the bolt goes into battery, AND the firing mechanism has time to fire the next cartridge.

In your theory, the barrel has to retain pressure while everything listed above is happening. I just don't see it. The timing is all wrong.

H

Food for thought...maybe the round just before this one was a squib or low-powder round?
That bullet would not have cleared the barrel before this one fired.
I'm not saying that's what happened, just one more possibility to consider.
In any case, I'm glad you are OK and nothing went KA-POW!

Thinking about trying an H3 buffer and different ammo.
Of course with extreme caution...

I believe that shell extracted before the bullet left the barrel. Why, is another question, but if it's a spring operated blowback, I'd try a stronger spring.

That doesn't mean I'm right. That's just where my mind goes, first reaction.

OK so the "going too fast" thing doesn't make sense to me. The bump fire doesn't go as fast as a real automatic. Watch this video. They use a real M-16, then use the Slide Fire. The slide fire version is going a lot slower.

Review: Slide Fire Solutions SSAR-15 Bump Fire Stock - YouTube

Originally Posted by mikeli

OK so the "going too fast" thing doesn't make sense to me. The bump fire doesn't go as fast as a real automatic. Watch this video. They use a real M-16, then use the Slide Fire. The slide fire version is going a lot slower.

Review: Slide Fire Solutions SSAR-15 Bump Fire Stock - YouTube

You are using the 5.56mm/.223 example when the problem is with a 9mm.

I know that the standard AR-15/M-16 fires with a locked bolt that has to be rotated before the round can be extracted. Very familiar with this firearm as I am the proud owner of several.

The 9mm versions are blow back operation and rely on the bolt/spring/buffer to prevent issues like this. In short, the cyclic rate has been exceeded and the case is still "pressured" when it is being extracted.