Just Right Carbine explosion

Alex Clayton said:

I have a few of the TNW's which from the outside look like the same rifle. Did the conversion just include a new bolt head? If so did it say anything about the buffer spring? It sure looks to me like as others mentioned the action is opening too soon. So not enough weight between the bolt, and the buffer spring combo. This is assuming the JR is the same internally as the TNW's. I can shoot 9mm, .45, and 10mm through mine with just different bolt heads but I have never seen the internals on the JR to see if they work the same. ??

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3 calibers with just a different bolt head? Didn't have to change the barrel? That is a neat trick.

MySuomi said:

I did notice that the next round up in the magazine had the bullet jammed deep into the casing. I was wondering if some how the bullet was getting pushed into the casing as the round was loading. Thereby causing a pressure situation.View attachment 948218

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Bingo.

MySuomi said:

Maybe. But, when i was function testing, the rounds all seemed to seat and the bolt seemed to be closing fully.

I did notice that the next round up in the magazine had the bullet jammed deep into the casing. I was wondering if some how the bullet was getting pushed into the casing as the round was loading. Thereby causing a pressure situation.
The round in the middle was the next round up in the mag. The one of the left was the second one. The one on the right is the spent round from the second shot. It has the bulged out primer.View attachment 948218

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That pic, the round looks like it's been hit hard, was it in the mag like that, as you mean next one up? If so it sure sounds like as another mentioned gas is hitting it. If it looked like that after clambering but not firing? Then it looks like it would be feeding issues. Something certainly hit that round and pushed the slug in further. If it is like that before clambering, it will create more pressure, then if the action is opening before the slug leaves the barrel? That would cause a KB.

denster said:

3 calibers with just a different bolt head? Didn't have to change the barrel? That is a neat trick.

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Someone always has to pretend to be dumb and not get it I guess. Problem is this just confuses many who can't see that someone is trying to play dumb and or be funny. At least I would hope you are playing but you never know. So just in case, yes, assuming the JRC is the same internally as the TNW look alike you of course get a different barrel for each caliber. The whole selling point of these is you buy one gun, the receiver is serial numbered. Then you can order parts to convert them to .22 LR, 9mm, .40 S&W, .45 ACP, 10mm ect. directly. If the JRC has the same internals they sell you just the bolt head that goes with a two piece bolt. The way a blow back operates is the weight of the bolt and weight of the recoil spring, which in the case of the TNW is a Mil-Spec Buffer Tube and spring. On mine the same buffer and spring works with 9mm, 10MM, and .45. The bolt head they sell is weighted to balance things out with no other changes in the action. I have not handled a JRC so do not know for sure it's the same inside, sure looks like the people who designed both used the same idea though.
So again this was why I asked the OP, did the conversion just come with a new bolt head, and say to use the same buffer spring already there. Reason being it looks like the action was being allowed to open before the round left the barrel which would create a KB.

MySuomi said:

The conversion kit contained the following:

• New Barrel
• Recoil spring and new buffer
• New mag well
• New bolt and carrier.

The buffer is pretty heavy and the bolt seemed to have a little more restricted movement than the 9mm.

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It will be interesting to see what the manufacturer has to say then, very strange. I would hope they ask for it back and replace it. If they do I hope they tell you what they think went wrong.

MySuomi said:

Maybe. But, when i was function testing, the rounds all seemed to seat and the bolt seemed to be closing fully.

I did notice that the next round up in the magazine had the bullet jammed deep into the casing. I was wondering if some how the bullet was getting pushed into the casing as the round was loading. Thereby causing a pressure situation.
The round in the middle was the next round up in the mag. The one of the left was the second one. The one on the right is the spent round from the second shot. It has the bulged out primer.View attachment 948218

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THAT is the problem right there. You are already dealing with very high pressure cartridge in 40sw. Bullet set back in these can subsequently DOUBLE the pressure!

denster said:

I still believe headspace is the problem. Did they give you instructions for headspacing the barrel when you did the caliber change?

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A pistol (40S&W)headspaces off of the case mouth, really can’t mess it up, unless the chamber wasn’t machined correctly.

Blowback designs don't ever really lock the bolt into the barrel or receiver. I've had bolt bounce (bolt bounces back rearward off the breechface as it slams forward into battery and is actually starting to extract the case as the hammer falls) cause several OOB issues in both a 45ACP and a 40S&W AR15 carbine that I'd build, with excessive reciprocating mass (in my case, a heavier-than-needed buffer) being the ultimate culprit.

I'd suspect an OOB due to bolt bounce and bullet setback before I even thought about a miscut chamber.

i'm with the setback issue. I had that with a CZ, normal recoil, louder than normal, different pitch, lots of smoke, spit some powder at me. Round underneath was dirty, but nothing blew out. CZ was fine. Don't expect anything from Remington.... as you know.

I know this sounds dumb and I'm sure you'd have noticed if it was wrong but any chance you have a 40s&w chamber in a 9mm barrel?

rbernie said:

Blowback designs don't ever really lock the bolt into the barrel or receiver. I've had bolt bounce (bolt bounces back rearward off the breechface as it slams forward into battery and is actually starting to extract the case as the hammer falls) cause several OOB issues in both a 45ACP and a 40S&W AR15 carbine that I'd build, with excessive reciprocating mass (in my case, a heavier-than-needed buffer) being the ultimate culprit.

I'd suspect an OOB due to bolt bounce and bullet setback before I even thought about a miscut chamber.

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I was trying to rationalize the headspace theory... Finding the round setback in the magazine, is a dead give away in my book.

Did you gauge the Bbl to make sure it was, in fact, .40... and not 9mm?




GR

MySuomi said:

No. The conversion kit had a clearly marked barrel labelled 40 s&w. And I plunk tested several 40 rounds to make sure they had case support. They did. I would not say perfect case support but it looked adequate. So that is probably not it.

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Might be beating a dead horse here, but stamping a barrel .40 S&W doesn't necessarily mean it is. cutting a .40 chamber into a 9mm barrel would allow it to pass a plunk test. I know pictures can be a bit odd, but the one you posted looks like a big step down from the chamber to the barrel - way more than what I see in the 9mm and .45 barrels I just checked.

DairyVet said:

Might be beating a dead horse here, but stamping a barrel .40 S&W doesn't necessarily mean it is. cutting a .40 chamber into a 9mm barrel would allow it to pass a plunk test. I know pictures can be a bit odd, but the one you posted looks like a big step down from the chamber to the barrel - way more than what I see in the 9mm and .45 barrels I just checked.

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You would think the bullet would be stuck in the barrel if that were the case.

Just to check, set a loaded round bullet down on the end of the muzzle. With that bullet profile the shell casing should rest on the crown.

Taurus 617 CCW said:

Another thing to look at is headspace as others have mentioned. The headspace for that round is based on OAL for the cartridge. Double check your barrel marking to make sure they didn’t give you a 10mm by mistake or anything else funny. It sounds to me like there was something wrong from the get go indicating that the condition never changed. My suspicion is the relationship between the bolt snd barrel.

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Shooting a 40 Short and Weak in a 10mm chamber would not cause this blowout. It's the same as shooting a 38 SPL in a 357 Mag.

OP,

Take a tight fitting jag and patch and run it through the barrel. Not all bulges will show on the outside. If there are loose spots where the jag and patch move through the barrel you've got a problem.

JDGray said:

You would think the bullet would be stuck in the barrel if that were the case.

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I would think so too, but I’ve been wrong often enough. And that looks like one heck of a wide shelf at the end of the chamber. Could be an odd photography artifact I suppose.

DairyVet said:

I would think so too, but I’ve been wrong often enough. And that looks like one heck of a wide shelf at the end of the chamber. Could be an odd photography artifact I suppose.

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I did notice that too!