.22lr case rupture, Ruger MKIII 22/45

Took my daughter to the range tonight, and ~75 rounds into her session her 22/45 locked up. I heard the round fire, saw a fresh hole in the target, but no case ejected. Dropped the mag to verify # of rounds remaining (as a sanity check that the round did indeed fire), but the bolt wouldn't budge so we packed up and headed home.

http://tinyurl.com/pbe236

http://tinyurl.com/rdz4vw

She's fired ~1000 rounds of this particular lot# in the past 1-2 months without incident (we have another ~3000 rounds of this lot remaining). I plan to forward pics to Federal to see if they've had any problems reported.

On the plus side, my little girl continues to have fun and work hard. She's been practicing press-outs, and tonight she got to run against a timed friend/foe target. From ready, press out @ 5yds, foe presented for two seconds (which I've learned is closer to three seconds with the way the target operates at the NRA range):

http://tinyurl.com/m7vm65

That lone shot outside the 8" circle was the round with the ruptured case...

I've had that happen recently with a new 10-22, using Remington Subsonic. In fact, it happened twice in about 200 rounds. Made me suspect possible chamber problem, but have not checked it any farther.

Skip

It's kind of difficult to get a good look into a Ruger .22 pistol chamber. You could remove the bolt and look from the rear of the receiver but I'd be tempted to cast the chamber with Cerrosafe and take some measurements of it. Were any of the other cases bulged?

If the chamber is within spec, I'd guess that the cartridge case was defective or thin in that area. If it was a double charge, obstructed barrel or something else that caused the chamber pressure to spike, I wonder where the weak point of the case would be for a .22 rimfire with a blowback action? Would it tend to rupture the side of the cartridge case or bulge/rupture the case head, especially where the firing pin aperture and extractor cut in the bolt face leave the case head unsupported?

Dave, I didn't think to check any of the other cases for bulges - I'll be sure to retain them during my next range visit for inspection.

This 22/45 is a few years old, with ~9000 rounds down range, so I'm leaning towards a fluke round vice newgunitis... We'll see :cool:

Over the last 40 years I have had the samething happen in a number of different .22's. I never found anything wrong with any of the firearms. I think it has been a "BAD" or "THIN" case. I had not noticed any loud reports or felt recoil increase so I don't think they were over charged. Just a 6 sigma failure. 3.14 issues per million opportunities.

Just got back from the range where I fired one 50rd box of Fed 510 (same lot # as the ruptured case above). Of the cases that I could grab (some went forward of the firing line) I had three more ruptured cases, none of which locked up the gun.

I'm taking my son to the range tomorrow, and I plan to run a box from this lot through his 10/22 and gather as much of it as I can. If I see split cases from a second firearm, then I may be onto something.

Additionally, I plan to run a few different brands of ammo through the 22/45 and collect as many cases as I can in an effort to eliminate the possibility that the chamber in my 22/45 has gone south.