Unsupported Chamber?

The recent group of threads about bulged cases and catastrophic failures has got me thinking about unsupported chambers. Several years ago the Glock suffered several of these catastrophic failures and much of it was attributed to the unsupported chamber. Even so, I don't know of any clear evidence that proved an unsupported chamber was the problem.

Recently I raised the question again when it was discovered that the Shield chamber/feed ramp design was significantly different than the compact or full sized models. This got me thinking so, I took a pic of several different pistol barrels to see what differences I could see:


From left to right:
Beretta 92FS 9mm, Browning Hi Power 9mm, M&P .40c, M&P .40 Full Size, M&P .45ACP Full Size, Ed Brown 1911 .45ACP.

I noticed a few things right off. Both the 92FS and Hi Power have unsupported chambers, but only a little. Both of the M&P .40S&W have not only fully supported chambers, but the case is actually below the mouth of the chamber. The M&P .45 full size has an unsupported chamber which surprised me, but there it is in full color. The chamber/feed ramp looks just like what I've see with the Shield only bigger.

What surprised me most was the Ed Brown. Here we see the case is not supported and I would even say that the unsupported part is at least 170° around. Even so, it's not that deep.

I also have an M&P 9mm full size, but forgot to include it in this pic. It looks just like the two .40s you see here. I can post a pic if you don't believe me.

Anyway, I have tens of thousands of rounds through the guns represented here. None have ever produced a bulged case or catastrophic failure. In fact, I reload the .45 and in about 5,000 rounds never had a case fail or bulge. I have seen cases split, but I believe that to simply be due to being reloaded multiple times.

I have seen some badly damaged cases in the .40, but those were not reloads and the explosion was fully contained in the chamber as it should be.

There is not enough here to draw any real conclusions. However, in my unscientific opinion, the unsupported chamber issue is not as bad as I thought. I still maintain that a fully supported chamber is better and more resistant to failure resulting in a destroyed gun.

Anyway, it's just food for thought.

.40 also operates at higher pressures than .45, so I'd imagine that'd be easier on brass in general.

Not to start an argument here but with a shell case in the chamber of my M&P .45, the entire case wall is supported. The only part that is not supported is the tapered area just in front of the head, and that portion of the case is much thicker and the pressure at that point is pushing back against the head.

gboling,
That is a good observation. It supports some of the other manufacturing variations suspected in other guns.

I don't have a picture, but I've had the old and new Glock .40 barrels in hand, and also compared 1911, Hi Po, and STI 2011 custom Open 9mm barrels.

The old Glock .40 barrels show a lot of brass in a smiley compared to the new ones.
As you noted, my Hi Po 9mm is about like the old Glock .40 barrel in the amount of brass showing, and the 9mm 1911 isn't much better. The STI barrel custom made for shooting 9mm Major (overpressure HS6) handloads is fully supported. When one of our shooters inadvertently put the 9mm Major loads into his 9mm 1911, we got a vivid demonstration of what happenes: he blew the magazine and a shower of brass out the mag well, but the metal gun was undamaged. Also showed why gripping "cup and saucer" endangers the off hand if a cartridge blows.

The old Glock 40's that went Kaboom were using 180 grain ammo. Lesser weights didn't seem to have this problem.

For those of us that have a Glock 21 converted to shoot .45 Super or a Glock 20 shooting 10mm, we know that if we're going to shoot hot loads, DON'T EVEN THINK ABOUT SHOOTING THEM FROM THE FACTORY GLOCK BARREL!
We immediately replace the OEM barrel with a Lone Wolf, KKM or Bar-Sto... Something that has FULL CHAMBER SUPPORT.
To have a KaBoom with one of these high powered pistol cartridges could be very dangerous.
Chamber support is a critical issue.
Obviously, with the Shield 40 as well.

unsupported chamber

I lost an M&P 45 from the unsupported chamber, I believe. Loaded 185 gr JFP with 6.6 gr Power Pistol. Blew down and out. Pulled every bullet in that reload sequence and everything measured exactly the same.No bulged primer. Use a Dillon x650 and check every third to fifth round. Do not load fast and try to be precise. S&W says it's me and not the gun, After seeing many articles, unsupported chambers are real and scary (having experienced one). I would think gun manufacturers would build for many different situations, including low side powered reloads. I know I am putting myself out there, but thoughts and opinions? One weird thing is the case was a Geco. Never seen or heard of them until I looked them up.

The unsupported chamber......

The unsupported chambers that cause a bulge was from the FEED RAMP being cut to far into the chamber. All of those pictures are fully supported. They head is the strongest part and the groove needs to be grabbed by the extractor.

The resulting bulge from an unsupported feed ramp was on the part of the case that was over the (missing) feed ramp space, consequently the bulge was on one side of the case and as wide as the feed ramp opening.

Excellent information! Thanks! What about 9mm M&P Shield models?
I knew about unsupported Glock problems, but are 9mm M&P Shield cases considered to be sufficiently supported? Regards...

Some relevant bits... someone out in internet land once took a great picture of how Glock .40cal pistol barrels evolved over years. They started with precious little case mouth support and the evolution was easily apparent. Not changed by gun generation and never announced or advertised as an improvement (even though it was a massive improvement.)

Also, guns and SAAMI specs for them are standardized for original gun with SAAMI-spec new ammo. After that, all bets are off. MANY of us use all our guns almost exclusively with handloads, and that isn’t what they were aiming for when they made them. So if a pistol successfully eats and runs factory ammo (but trashes the brass horribly) then that is “acceptable” as the industry goes. Even though that isn’t acceptable to me and to most handloaders. It’s definitely a reason that I wouldn’t keep my Delta Elite.

Along with that point above, some handloaders will use a “bulge buster” where they take GLOCK’d up dangerous brass and run it through a case sizer to push the displaced brass back in to form.

As a serious handloader that keeps the quality of his ammo and process in extremely high regard, I believe this exercise is unsafe and ill-conceived.

I’m no metallurgist but seems to me that when cartridge brass gets displaced under 35-37.5k psi and extreme, irrational heat, I don’t believe that forcing it through a die at 70 degrees F restores the structural integrity of the cartridge case.

After seeing a fellow competitors Glock destroyed from a blown round I’m a huge believer in fully supported chambers. I don’t own a Glock but most of my 1911’s have fully supported chambers.

As to the bulge buster, brass is too cheap to risk an accident.

OKFC05 said:

I don't have a picture, but I've had the old and new Glock .40 barrels in hand, and also compared 1911, Hi Po, and STI 2011 custom Open 9mm barrels.

The old Glock .40 barrels show a lot of brass in a smiley compared to the new ones.

Click to expand...

I've bought a G27 when they first came out, and always
wondered about the redesign for more case support, in
later production.

At any rate, Glock is getting called on it...class action here:

https://www.classaction.org/media/melian-et-al-v-glock-incorporated-et-al.pdf

Sevens said:

Some relevant bits... someone out in internet land once took a great picture of how Glock .40cal pistol barrels evolved over years. They started with precious little case mouth support

Click to expand...

Methinks you confused your terms a mite. The case MOUTH-at least in common usage-is where the bullet is. One would hope that area was fully supported.

I believe the term you were looking for is case head/web.

Just a sanity check...

Y'all realize this thread is 6 years old, right?

EXCELLENT Point! I did not catch that! Anyhow, today I disassembled my recently acquired M&P 9mm Shield 1.0 and checked the cartridge support. It appears adequate...maybe a 1/32nd or less of the base exposed. Your reminder to check the vintage of a thread is genuinely appreciated. Regards...

I also didn’t notice it was a necro-thread. Still seems to be a decent conversation. We do that... right?!

Yes, I meant case head and not case mouth.

Rastoff said:

Just a sanity check...

Y'all realize this thread is 6 years old, right?

Click to expand...

So we're bored.

Rastoff said:

Just a sanity check...

Y'all realize this thread is 6 years old, right?

Click to expand...

I thought it was old with someone still using photobucket pics

You know you're bored when you don't notice the post date until you've read post #15...
6 years , My Lord !

Truth is I've read every gun magazine in the house ...twice and some go back to 1977 .
Guess I'll read "Sixguns" again...or look at the pictures !
Gary