Just Right Carbine explosion

Discussion in 'Rifle Country' started by MySuomi, Oct 12, 2020.

  1. denster

    denster Member

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

    jimboecv Member

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    Bingo.
     
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  3. Alex Clayton

    Alex Clayton Member

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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.
     
  4. Alex Clayton

    Alex Clayton Member

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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.
     
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  5. MySuomi

    MySuomi Member

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    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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  6. MySuomi

    MySuomi Member

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    Yes they did. It is hard to describe the "funny" sound. They went bang hard and loud. It just sounded a little off. Hard to explain. But they did seem to be working the gun's action.
     
  7. MySuomi

    MySuomi Member

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    Thanks for the insight guys. I tried to read thru the answers and post some general replies that added some of the missing info.
    I inspected the barrel last night. It looks fine. I can see no evidence of a squib round being pushed out.

    I am leaning toward the headspace problem or somehow the bullets are getting jammed into the case due to the blowback action. Maybe even some issue with the bolt not behaving correctly. IMG_2121.JPG IMG_2124.JPG IMG_2125.JPG IMG_2126.JPG IMG_2129.JPG IMG_2130.JPG IMG_2131.JPG

    Here are the barrel pics as best as I could get them:
     
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  8. Alex Clayton

    Alex Clayton Member

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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.
     
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  9. David Hoback

    David Hoback Member

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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!
     
  10. JDGray

    JDGray Member

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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.
     
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  11. rbernie
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    rbernie Contributing Member

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    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.
     
    Last edited: Oct 13, 2020
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  12. mjsdwash

    mjsdwash Member

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    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.
     
  13. CarJunkieLS1

    CarJunkieLS1 Member

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    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?
     
  14. Spats McGee

    Spats McGee Moderator Staff Member

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    I can't wait to find out how the mystery ends!
     
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  15. JDGray

    JDGray Member

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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.
     
  16. Garandimal

    Garandimal member

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




    GR
     
  17. MySuomi

    MySuomi Member

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    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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  18. MySuomi

    MySuomi Member

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    Thanks again for all of the suggestions. I am leaning toward the headspace or out of battery being the issue. Once I get some feedback from JRC I will let everybody know.
     
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  19. DairyVet

    DairyVet Member

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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.
     
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  20. JDGray

    JDGray Member

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    You would think the bullet would be stuck in the barrel if that were the case.
     
  21. Englishmn
    • Contributing Member

    Englishmn Member

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    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.
     
  22. MySuomi

    MySuomi Member

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    Ok, will do. I thought my plunk test would cover it but that is a good point about that being more of a chamber test instead of a barrel test. Will do another test tonight to verify the barrel.
     
  23. Cannibul

    Cannibul Member

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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.
     
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  24. DairyVet

    DairyVet Member

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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.
     
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  25. JDGray

    JDGray Member

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    I did notice that too!
     
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