Powder propelled mag eject. Twice

[Stealsack]

 

So, a friend of mine has a 2 month old RIA tac ultra 9mm.

A few weeks ago the gun rather exploded in his hands. It blew the corners off the hand grips, burnt his hands a bit, singed his face, and toasted a mag.  No witnesses.

Now he is newish to reloading and wasn't really aware to watch his range brass for cracks. The recovered case was blown out a bit above the base, about where I've seen other brass crack.

I was pretty sure that he loaded a cracked case and had an unusual failure. Case er, closed.

So it was a surprise when during a match yesterday he had another very fast mag change. This one we have on video from two cameras.

I'm surprised because I "supervised" him loading the rounds on my 1050.  I can definitively say that there were no double charged rounds.

The powder I was using overflows in a double charge and I was watching even closer that I would if I were loading myself.

The failure on camera sounds a bit different because of the energy going down as well as forward, but not louder. I was his RO, and I heard it, but it was not very noticeable. Not like a squib or overcharge. The round prior went down range as did the failed round.  Not a driven squib.

On the video you can see that the slide only came back about 1/4 to 1/3 of the normal motion.  No brass ejected out of the port that I could see.

Checked the barrel clear, at the safety table and put him back in for the next stage.

Round wouldn't chamber. Looked really closely and there was a brass ring normal thickness and 3/16" wide that looked to be cut with a tube cutter still in the chamber. Very nearly perfect cut around the circumference up tight to the end of the chamber. Had to remove that on the work bench after the match. It was essentially invisible as it just looked like the chamber step.

I'm not sure what to think at this point. I have had a case fail while shooting, I heard it hit the ground, it made a very distinct sound and was cracked from the mouth downward. No drama.

The gun is stock but for a little polish and an Aftec extractor.

Why would his gun fail twice in such a spectacular fashion?

Video can be available if it will help diagnose the issue.

I feel like I'm missing something obvious. I suppose that it could be two really rare occurrences that my brain will not accept as rare because they were close together, but I'd rather not ignore the warnings.

Thoughts? 

 

 

 

 

[drewbeck]

What type of brass and caliber? It’s probably either a stepped case or very unsupported chamber, or potentially out of battery ignition.

[CHA-LEE]

That sounds like a chamber diameter (too large) or unsupported case at the top of the feed ramp situation. If the chamber diameter is too large then the brass must handle and contain the whole explosion. In a properly sized chamber it should only be slightly larger than the brass that way the brass can expand to the size of the chamber and not fail. If the bottom portion of the case is not supported because the feed ramp is cut too far forward its the same situation. The explosive force is going to travel towards the path of least resistance.

 

I would suggest that you take some case diameter measurements in several locations along the length of the brass on a loaded round. Then shoot it in the gun, recover the brass, and redo the measurements. If the brass has been expanded dramatically then you have found the problem.

[CHA-LEE]

I also wanted to point out the obvious that since this is 9mm there is the chance that he is using stepped brass where the internal volume of the case is dramatically reduced. You don't need a double charge in a stepped case to create a compressed load scenario which can lead to a "KABOOM" with certain powders. The "Ring of brass left in the chamber" is a tell tail sign of using stepped brass. When those cases fail the section of case above the step usually separates from the base and stays lodged in the chamber.

[Stealsack]

Nice, thanks for the quick response.

I didn't think stepped brass would go through my machine, at least not without feeling very different, but now I will have to test that.

It would certainly fit the facts. It is a VERY clean-cut ring.

I don't really check for them except by sound, into the washer, into the dryer, into the tray, into the hopper. I hear steel, cracks, the odd case that just sounds wrong but looks ok.

If I had one make it into the press I never noticed. Yikes!

I'll measure some shot brass tomorrow CHA-LEE and see how it compares. That makes sense. I should have thought of that.

28 minutes ago, drewbeck said:

What type of brass and caliber? It’s probably either a stepped case or very unsupported chamber, or potentially out of battery ignition.

RIA tac ultra 9mm.

Mixed brass. Certainly possible that a stepped case slipped through.

The gun looked like it was in battery at ignition on camera, but you know...

 

 

 

[Sarge]

1 minute ago, Stealsack said:

Nice, thanks for the quick response.

I didn't think stepped brass would go through my machine, at least not without feeling very different, but now I will have to test that.

It would certainly fit the facts. It is a VERY clean-cut ring.

I don't really check for them except by sound, into the washer, into the dryer, into the tray, into the hopper. I hear steel, cracks, the odd case that just sounds wrong but looks ok.

If I had one make it into the press I never noticed. Yikes!

I'll measure some shot brass tomorrow CHA-LEE and see how it compares. That makes sense. I should have thought of that.

RIA tac ultra 9mm.

Mixed brass. Certainly possible that a stepped case slipped through.

The gun looked like it was in battery at ignition on camera, but you know...

 

 

 

Stepped cases feel and feed through presses exactly like any other brass.

[Stealsack]

 

5 minutes ago, Sarge said:

Stepped cases feel and feed through presses exactly like any other brass.

 

I guess some do (obviously)  but the only time I caught one trying to sneak through, it stopped on either the decap or the primer resize, I don't remember which.

It was like hitting stainless media in the primer pocket, you FEEL it when it happens.

It could be that many have made it through or that I get very few from my brass bandit. I'd guess the latter, as while I don't sort by headstamp, I do look at the brass pretty hard several times before it gets loaded, and I have only had to toss a few.

[Stealsack]

As a follow up.

Measured 6 cases from rounds in the magazine left over from the match ammo.

Measured each case three places, just after the rim, mid-point, just back from the mouth.

Marked the cases and fired, recorded each case measurement again.

Loaded - Min/max across all 6 cases.

Case rim: min-.385 max-.388

Mid-point: min-.372 max-.375

Mouth: min-.374 max-.377

 

Empty Brass

Case rim:  min-.389 max-.390

Mid-point: all were exactly .390

Mouth: The mouth of the cases were slightly out of round with the largest min/max being .380-.386 on the same brass

I didn't measure any out of round or bulges at or near the base of the cases.

I expect that this makes a "stepped case" the likely cause of the failure. 

Thanks all for the input! I'll have him inspect cases before loading and have him shoot the gun.

 

[CHA-LEE]

SAAMI Case/Chamber diameter spec for 9mm Luger is listed below. As you can see there isn't much of a size difference between the outer diameter of the case and the inner portion of the chamber. Your before shooting measurements are consistent with what a reloaded round that is slightly undersized by the sizing/decapping die would do. The empty brass measurements are very close to matching the SAAMI spec and it doesn't look like you have an out of spec chamber. Root cause of the "KABOOM" events is likely stepped brass.

 

SAMMI Spec for Case

Bottom just above the rim groove 0.3910"

Mouth at the top end of the case 0.3811"

 

SAMMI Spec for Chamber

Bottom just above the rim groove 0.3913"

Mouth at the top end of the case 0.3820"

[ATLDave]

[echotango]

Working on a die to find stepped brass.  It will be located at the primer station on a 1050.  The press will stop if stepped brass is present.  

[Stealsack]

20 hours ago, CHA-LEE said:

Root cause of the "KABOOM" events is likely stepped brass.

 

Thanks Cha-Lee, as always your advice is much appreciated!

 

@ATLDave Hahaha! Indeed!

 

@echotango That would be slick. My 1050 did find one that slipped through, but after looking at many examples, I can see how many could make it past my current setup.

Hit me up when you are ready for testing or production!

 

 

 

[echotango]

22 minutes ago, Stealsack said:

 

 

@echotango That would be slick. My 1050 did find one that slipped through, but after looking at many examples, I can see how many could make it past my current setup.

Hit me up when you are ready for testing or production!

 

 

 

I will post it once it is done and works.  I look at my brass after it is cleaned but it gets old looking at 10k at a time.  This will hopefully make it a lot easier as they do slip by once in a while.  I then find them when gauging as the head stamps stand out to me.  But rather have something a little more fool proof. 

[223to45]

I have had a couple step brass slip through my 650.

I only noticed because I run 165 grain. If I was running 115 I probably wouldn't have noticed, until it was to late.

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[theWacoKid]

First event sounds like used up case in an unsupported chamber or slightly out of battery firing.  The out of battery thing is more often than not the catalyst for a nice base blowout.  

 

The second is a stepped piece of brass that breaks all too common exactly as you say.  Geometry and stress concentration is the root cause and not pressure.

 

Cull all FM, Ammoload, and IMT headstamps and make sure the gun gets into battery.  

[Hi-Power Jack]

Any chance it was a bullet being pushed back into the case, and 

drastically reducing the OAL of the round ?   (Bullet setback).