What caused this bulge in the 9mm Luger shell case?

[martyd]

9mm Luger Case

I refer to this as a pregnant shell case.

There is a bulge at the base of the case which is quite noticeable.

I appears to me that the case is not chambered all the way when firing.
Which could happen with a full automatic firearm.
OR
There is a defect in the barrel chamber.

I see this fairly often on range brass.

Sorry I couldn't get a good pic from the side.

Any idea what causes this?

[Bazoo]

Maybe a weak recoil spring. The gun is cycling before the pressure drops, coupled with a mark from the slide hitting the brass.

[358429]

My opinion is that brass fire formed to seal the feed ramp. Is there any damage to the mouths or rims of these bulged cases?

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[Dusty Bannister]

Looks like soft brass case that is loaded to higher pressures. Look at the primer and it will appear to be a narrow rectangle, and a tear drop shaped imprint from the firing pin. Usually resulting from higher pressures in an inadequately supported chamber. More often seen in early Glock 40's. What is the head stamp on the case?

[USSR]

Dusty has it. Fired in a Glock.

Don

[Pine Baron]

Dusty and USSR are onto it. Very common with Glocks. Full size die and go.

[downzero]

Maybe a weak recoil spring. The gun is cycling before the pressure drops, coupled with a mark from the slide hitting the brass.

Locked breach guns do not depend on the recoil spring to keep the gun in battery. The spring is just to store energy to push the slide forward and chamber another round. In theory they can be safely fired without the recoil system even installed at all.

[Martin Luber]

Unsupported chamber in a Glock, do not reload these.

[FLINTNFIRE]

Do not reload them is the best advice , was not just glock who made unsupported chambers , do not bulge bust them either there is a weaked section now and all resizing does is try to make it less obvious .

[Dusty Bannister]

I did not want to brand this case as having been fired in a Glock, but just that is where they are commonly encountered in some calibers. This has also been found in inexpensive 380 ACP guns and I would also wonder about some of the pistol caliber carbines since the longer barrels will have higher pressures due to barrel length. Until the OP provides more information, it is only speculation.

Make NO attempt to reload these weakened cases!

[Conditor22]

the Glock bulges I've dealt with didn't have that dent. Looks like it hit something on its way out of the chamber.

[RobS]

Looks like there may be some good expansion at the head and then a ding likely from the ejection port making things look worse or more bulge than what there is.

[DocSavage]

Those cases don't look like any cases I've seen fired from a Glock. Bulge is way to big.

[charlie b]

The 'smile' ding is typical from the cases being hit by the slide. I've had them get that in my 1911's, but, not with that huge bulge.

Now that I ponder the issue I seem to remember similar cases from some M3 submachine guns (also .45acp and 40 years ago).

[Dusty Bannister]

Charlie, that is why I was asking about the appearance of the primer. The older guns like the Thompson 1927, shooting 45 acp had a large firing pin and was quite a bit different from any other impression. Yes, there is a reason for asking these questions when photos are not submitted. And given the fact that these fired cases are from AZ which is pretty warm this time of year, it might result in higher pressures than rounds fired in "normal" temperatures. It would also be helpful to see different views of these cases and also to be told if this is the recovered appearance or after running through a brass cleaner.

[bedbugbilly]

At the easy availability and cheapness of 9mm range brass - why would anybody want to FL size these and use them . . . . toss 'em in the scrap bucket and use a casing that hasn't been stretched out of shape. Not an answer to the OP's question but rather a response to anyone who would consider re-using bulged 9mm.

[reloader28]

Funny, I've reused bulged brass and not had a problem.

[charlie b]

I have as well, just not bulged over that large an area. A bit different with the .45 though, it being a fairly low pressure round with a 'lot' of tolerance in case volume.

9mm I am a bit picky about. Small cases, relatively high pressures. Small changes make big differences.

[gwpercle]

Just run them through the Lee "Bulge Buster" ...takes that belly right out ...
the kit sells for about $20 .
Gary

[358429]

The sharp crease in the brass looks like a case head failure waiting to happen.

I would not reload these, with out a most thorough inspection, which they may not be worth the time.

So...When a pistol is engineered correctly and the slide/barrel are in battery (locked together) the firing pin is capable of striking, and explodes the primer. Pop.

The powder burns rapidly and creates an expanding volume of hot gases, which push equally in all directions.

This seals the brass to the firing chamber, fire forming it, functioning as a gasket.

The bullet is the path of least resistance, and starts travelling, exchanging the energy/pressure from the gas volume into bullet kinetic energy.

Remember : equal and opposite force, the combined energy of accelerated projectile and powder ejecta leaving the gun, is pushing back, ultimately against the receiver or frame, which is in your hand.

This is the basic function of recoil based operation. Limp wrist a recoil operated pistol and you rob the energy required to properly cycle.

The barrel and slide move together a very small distance, then the barrel tips up (or the chamber cams down,depends how you see it) mechanically permitting the slide to unlock from the barrel, allowing the slide to move to the rear and extract the fired casing, and start over again.

The browning tilting barrel used on so many recoil operated pistols is a timing event.

Bang.
The bullet and powder gasses are long gone downrange if the pistol is correctly timed.

The guppy belly happens when the brass fire forms to fit to the feed ramp, and seal the pressure.

(Dummy with a dremel or glock smile, eh whos to say)

You can slow the slides reciprocation cycle speed by recutting the cam angles on the barrel hood/slide interface and or adding a muzzle break to redirect force from the gasses and add muzzle weight, or make the slide heavier, changing the lock/unlock relationship.

I am looking at you 460 rowland, and 9mm major!

Remember the brass is a gasket. Don't ever expect to use a creased metal gasket and have it be as strong and resilient as one undamaged.

That looks like brass I have found that I suspect was 9mm major overloads. That is why I was asking before, to check the rims and case mouths for damage that happens when slide velocities are too high.

P.s. I have attached a link to youtube, a small movie for your viewing pleasure.

Be safe.


---ORIGINAL PRODUCTION INFORMATION--- WAR DEPARTMENT Official Training Film Fundamentals of Small Arms, PART II: Types of Operations T.F.9 1449 ARMY SERVICE FORCES Produced by Army Pictorial Service, Signal Corps

https://youtu.be/vqUgvoVXqg0



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