Any specs on how much to break the edge of the FP hole?
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Thread: Any specs on how much to break the edge of the FP hole?

  1. #1
    Rifleman rusirius's Avatar
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    Any specs on how much to break the edge of the FP hole?

    Okay, so here's the deal. I've waited a couple of days for a response from RA, but haven't gotten one yet. In the mean time I'm getting impatient. No fault of theirs, and I know they're in the middle of changing things around or something, but I'm just completely impatient when it comes to stuff like this, so here I am...

    I've got an XCR that from day one has been piercing the occasional primer. I've been fortunate enough to never have one get up in the chamber and cause any problems, but it has been a real pain in the arse when every 7 or 8 rounds the thing misfires due to a slug of brass covering the FP.

    I normally shoot PPU XM193, and have also tried PMC and have the same issue (though it seems slightly less often with PMC).

    After contacting RA about it, they told me that it was an easy fix, I just had to send them the bolt. That's awesome... Except for one thing...

    I shoot this damn rifle just about every weekend.

    So after doing some research on here I found that the problem is the edge of the FP hole in the bolt. I'm familiar enough with machining that I'm fairly confident I can do this on my own in about 30 seconds. The only thing is, I don't want to f*[email protected] my bolt up, so before I do so I'm hoping SOMEBODY can give me something to go on as far as just how much chamfer should be on it. Are we talking about taking a thousandth off? A few thousandths? A few hundredths? And likewise is there any preference as to the angle?

    Just guessing I'd say probably about a 75 degree angle and leave a chamfer about a thousandth or maybe two wide. But that's completely a guess and I'd rather not play "guess" with my bolt!

    So is there anyone who has either had this done or knows enough to be able to give me some rough specs as to how much to take this thing down?

  2. #2
    Marksman paladius's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    I'm guessing you have more than one gun, so why not give the XCR a vacation and send RA the bolt? When you get it back, you'll see how much to take it down and know for the next time.

  3. #3
    XCR Guru aziator's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    XCRmonger might know the answer to this, I would PM her. I honestly don't recall it being mentioned here, just that it needed to be done to some bolts.
    Don't confuse enthusiasm for competence

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  5. #4
    XCR Guru Sean K.'s Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    Yep...try XCRMonger. Also, do a search....it may be more than just a firing pin hole that's the problem. I seem to recall someone else mentioning that chamfering didn't solve the problem.


    Here's an idea....buy a spare bolt.....(you should probably have one anyway) from Kermit Zahm at Wild Thangs Farms in Idaho (just search his name on this site for contact info).

    Get your bolt from Kermit....then send the out of spec one back to RA.....then you don't have any down time.

    HTH,
    Sean
    "Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger

  6. #5
    Rifleman Gregchico's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    My 5.56 bolt had a similar issue from the factory where it would sometimes pierce American primers or any 5.56 rounds, but would only crater Russian stuff. I had the proper chamfer on the bolt face and it turns out that my firing pin channel in the bolt was just a little to deep/long. They swapped out the bolt after I sent the bolt and barrel in for inspection. The total turnaround time was about 2-3 weeks. I have had zero problems since.


  7. #6
    Rifleman rusirius's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    Quote Originally Posted by paladius View Post
    I'm guessing you have more than one gun, so why not give the XCR a vacation and send RA the bolt? When you get it back, you'll see how much to take it down and know for the next time.
    More than one gun yes. More than one XCR? No... LOL... In all seriousness it is my only black rifle and the one I shoot WAY more than anything else... Let's be realistic here, it's not that I CAN'T go without it for a couple of weeks, it's just that I'd rather NOT if it's something I can bang out in my garage in 30 seconds...

  8. #7
    Rifleman rusirius's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    Quote Originally Posted by Sean K. View Post
    Yep...try XCRMonger. Also, do a search....it may be more than just a firing pin hole that's the problem. I seem to recall someone else mentioning that chamfering didn't solve the problem.


    Here's an idea....buy a spare bolt.....(you should probably have one anyway) from Kermit Zahm at Wild Thangs Farms in Idaho (just search his name on this site for contact info).

    Get your bolt from Kermit....then send the out of spec one back to RA.....then you don't have any down time.

    HTH,
    Sean
    I'm hoping it's not something else too, but at the very least I can try it first before being resigned to sending it in.

    Good idea on the bolt, but my understanding is that the XCR bolt is a bit on the pricey side. Maybe I'm being a bit naive, but I've NEVER broken a bolt in a firearm. Firing pin yes... Bolt no... So I'm having a hard time convincing myself to spend a fortune on a spare bolt that will basically only get used this one time... I suppose I could always sell it afterward... It'd be really nice if RA would send me a replacement bolt and I just send them mine back... From what I've seen they used to operate like that all the time, but from remarks here and there I've noticed it appears things might not be that way anymore. Kinda a shame really. I still haven't heard back from them, I'm hoping they're working a show and will get back to me soon...

  9. #8
    XCR Guru WatchoutforStobor's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    When my first XCR arrived and didn't work very reliably I got in touch with Terra through the forum. With a few emails back and forth we decided it was a bad bolt. She threw one in the mail and it took care of the problem.

    It's too bad that they don't have a "Terra" there anymore. I feel for you and know your frustration. I wouldn't send it back until you have contacted a real human at Robarms (not the anonymous "Tech") and they are expecting it and will give you updates.

    Good luck!

  10. #9
    XCR Guru Carpenter's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    I echo Sean, get an extra from Kermit. (Then, I think, do the chamfer on your old one yourself, rather than send it in)
    Depending on what you want the rifle for, an extra could be invaluable in the case of a broken firing pin.....I would also order a firing pin or two as they are cheap(ish).
    If getting your rifle running again quickly and easily in the event of a broken firing pin is not important, there are a few close up photos on here that you could look at.
    hope for the best, prepare for the worst, and make hay while the sun shines!

  11. #10
    Rifleman rusirius's Avatar
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    Re: Any specs on how much to break the edge of the FP hole?

    I don't really use my XCR for home defense, have plenty of pistols for that. I suppose in the event of a Zombie attack an extra bolt might come in handy, but since target practice is about all the duty my XCR sees I just can't justify the expense just to make an FP failure a quicker swap.

    BUT!!! I do have some great news! My XCR is now firing much more reliably. I milled a chamfer in just barely breaking the edge. The chamfer is probably about two-thousandths thick. Just enough to reflect a glint of light and that's about it. I turned the gas off so I could inspect the brass. Went through 3 boxes of PPU which was the worst at doing it. Usually I could cut a slug out ever 9 or 10 rounds. Made it through the whole 60 without a single slug. The primers actually showed a slightly raised area around the FP hole and defined the chamfer very well. No slugs so I'm quite happy!

    On the down side, it still wasn't 100% reliable. I still had about 10 misfires in 120 rounds. In these I checked very carefully that there was no brass plugs and there wasn't, but the primer showed a light hit. I realized then that this was most likely due to my own stupidity.

    When doing the chamfer I cleaned out the bolt really well to make sure no little itty bits of metal got down in the FP hole. Secondly upon finding the firing pin had rolled off into a dirty mess, I cleaned it up really well....

    Then proceeded to put it back in the bolt, and re-install the bolt with absolutely no lube... :duh:

    I'm sure once I strip it down and get it lubed up nicely again it'll be just fine. If not, I really want to get the trigger upgrade anyway, so I'm sure that will solve it...

    Thanks again for all the suggestions!

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