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Thread: FTF with New Gun (Pics) *Update on p.3*

  1. #41
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    Hello again.

    So 30% of the time the bolt failed to lock open on a empty magazine?
    That's correct. To answer your other question, I haven't done anything to the carrier key bolts.

    Unfortunately, I didn't get to try your bolt catch test (too late - see below), but will keep it in mind just in case.

    Might be camera angle but the mag does look just a slight bit "whacky" up at the feed lips. They aren't bent at all?
    I know- looking at the photo, it does look weird. But no, I swear to you, eyeballing them, they look fine.

    rero360, I did install the M4 RAS myself, but properly installed, I don't believe the little clamp that engages the barrel nut could really do any damage. I did look at that area of the gas tube, but it's fine.

    So BCM agreed to take a look at the upper. They'll get it on the 19th. I am glad of this, because they would be able to determine conclusively anything about the gas system, whereas I would not. And one way or another, what I hear from them will either confirm my suspicions, or simplify any further troubleshooting.

    I'll update the thread when I hear something.

  2. #42
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    I had the EXACT same thing happen to me with my BCM upper. When I installed my rail I didn't do it exactly right so the delta nut wasn't flush and the bottom of the top half of the nut was resting on the gas tube (if that makes sense, if it doesn't...the rubber part that would be near the gas tube was in contact with it). That probably bent the gas tube which prevented the bolt from cycling all the way back. I sent it back to BCM and they fixed my oops and they had it back to me as fast as shipping would allow.

  3. #43
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    bfk4lyfe, thanks for the input, but I don't believe our problems were the same. If my gas tube were out of alignment to the carrier key, the bolt would have problems going to battery. My problem now is that it goes to battery just fine, but without a cartridge in front of it.

    A further thought on this problem. At first, the factory new bolt was picking up cartridges from the side of the case, and causing them to go nose-up into the chamber, with the bolt wedged against the cartridge case. Considering all the brass buildup on the surface of the lower bolt teeth and carrier, does it not seem like the brass has in effect lubricated the metal surfaces of the bolt teeth? That would explain why on my second outing, I didn't have any bolt-overs with the cartridge being partially stripped off the mag. I only had the bolt slipping right over the top round in the mag without stripping it out. Again, this would indicate that the rearward travelling bolt isn't clearing past the case lip. Only, that when there was enough friction between the bolt surface and the top round, the round was able to be partially stripped out, and subsequently misfed (see the marks on the brass in the first pictures I posted on page 1). Ergo, undergassed.

    Also, why more failures with the M193 than the two 75gr loads? Because the heavier, slower bullet allows more dwell time for the gas before it leaves the muzzle. Another reason to suspect it's a gas issue. That's my thinking, anyway.
    Last edited by mr_blond; 12-14-11 at 23:11.

  4. #44
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    Quote Originally Posted by mr_blond View Post
    Hello again.



    That's correct. To answer your other question, I haven't done anything to the carrier key bolts.

    Unfortunately, I didn't get to try your bolt catch test (too late - see below), but will keep it in mind just in case.



    I know- looking at the photo, it does look weird. But no, I swear to you, eyeballing them, they look fine.

    rero360, I did install the M4 RAS myself, but properly installed, I don't believe the little clamp that engages the barrel nut could really do any damage. I did look at that area of the gas tube, but it's fine.

    So BCM agreed to take a look at the upper. They'll get it on the 19th. I am glad of this, because they would be able to determine conclusively anything about the gas system, whereas I would not. And one way or another, what I hear from them will either confirm my suspicions, or simplify any further troubleshooting.

    I'll update the thread when I hear something.
    No worries, I've installed a set or two myself, they do seem to be just about joe proof. Definitely wasn't a knock against your abilities, just trying to present alternative possible sources of problems. It is intriguing though, please let us know what BCM finds out, curious minds and all that.
    [SIGPIC][/SIGPIC]

  5. #45
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    Update

    I received my upper back on January 5th. Looks to be a completely new upper, as I didn’t see all the brass marks that were left on the bolt carrier assembly and the shell deflector from last time.

    I put the upper back on my lower, and took it to the range for some testing. The only two types of ammo I have right now are the same HSM 75gr 5.56, and the Guat M193. I started with a bunch of the old Guat M193. Filled two 30-round Pmags with it. Everything cycled fine while firing, but still noticed the bolt failed to lock back after the last round of one of the mags. So the rest of what I did for that range session was to check on bolt lockback by loading rounds both one and two at a time for each magazine.

    Out of 50 rounds of the HSM 75gr, loaded one at a time, the bolt locked back every single time.

    Out of 30 rounds of Guat, loaded two rounds in the mag each time (15 chances to observe the bolt locking back), the bolt failed to lock back on an empty mag 4 times.

    I switched to a standard carbine buffer, and did the same test with 30 more rounds of the Guat. Two at a time. Another 4 failures to lock back out of 15 chances.

    Well, there were no bolt-overs at all this time. That’s great. Also, the only times the bolt didn’t lock back on an empty mag were with the Guat ammo.

    Bolt lockback failure:
    Guat: 27% (30 tries)
    HSM: 0% (50 tries)

    So I will still have to try different loads going forward, but that seems like good news. Hopefully I can blame the ammo. I just ordered some IMI M855, and have several different types of 5.56 stashed elsewhere (long drive), so I’ll have to look forward to that.

    BCM was prompt and responsive, and I couldn’t have asked for more from them on the customer service side.
    Last edited by mr_blond; 01-15-12 at 17:57.

  6. #46
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    My past experience with the Guat surplus is that is is good, stout, true 5.56 spec ammo and suprisingly accurate.
    My brother saw Deliverance and bought a Bow. I saw Deliverance and bought an AR-15.

  7. #47
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    What buffer are you using now?

    Quote Originally Posted by mr_blond View Post
    I received my upper back on January 5th. Looks to be a completely new upper, as I didn’t see all the brass marks that were left on the bolt carrier assembly and the shell deflector from last time.

    I put the upper back on my lower, and took it to the range for some testing. The only two types of ammo I have right now are the same HSM 75gr 5.56, and the Guat M193. I started with a bunch of the old Guat M193. Filled two 30-round Pmags with it. Everything cycled fine while firing, but still noticed the bolt failed to lock back after the last round of one of the mags. So the rest of what I did for that range session was to check on bolt lockback by loading rounds both one and two at a time for each magazine.

    Out of 50 rounds of the HSM 75gr, loaded one at a time, the bolt locked back every single time.

    Out of 30 rounds of Guat, loaded two rounds in the mag each time (15 chances to observe the bolt locking back), the bolt failed to lock back on an empty mag 4 times.

    I switched to a standard carbine buffer, and did the same test with 30 more rounds of the Guat. Two at a time. Another 4 failures to lock back out of 15 chances.

    Well, there were no bolt-overs at all this time. That’s great. Also, the only times the bolt didn’t lock back on an empty mag were with the Guat ammo.

    Bolt lockback failure:
    Guat: 27% (30 tries)
    HSM: 0% (50 tries)

    So I will still have to try different loads going forward, but that seems like good news. Hopefully I can blame the ammo. I just ordered some IMI M855, and have several different types of 5.56 stashed elsewhere (long drive), so I’ll have to look forward to that.

    BCM was prompt and responsive, and I couldn’t have asked for more from them on the customer service side.



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  8. #48
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    Right now, I'm using the H2 buffer that came with the lower.

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