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Posted: 6/15/2011 1:18:30 PM EDT
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Well my new 11.5" SBR build is still having a problem with the bolt not staying locked back after the magazine is empty. My rifle is built with the following parts,
LMT lower with their 2 stage trigger, SOPMOD with 'H' buffer 11.5" BCM BFH upper with a RRA semi auto chrome BCG, PRI charging handle I have used 20 and 30 round PMAGS and new Colt 30 round mags with Federal M193 and M855. I have shot with my Gemtech HALO and without. The bolt will lock back with a 30 PMAG without the can on. I have lubed the rifle completly with Break Free and the bolt latch moves freely. Anyone have any ideas? Full Auto BCG? Or an H2 buffer? Thanks for any help |
| Is this a complete BCM upper or did you just use one of thier barrels (I did not notice BCM stamped on the side of the receiver)? If you just used one of thier barrels who pinned the FSB? I would call them or BCM if it is a complete BCM upper. Did you check the gas key on your BCG to make sure it is tight and staked? |
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Quoted:
bolt not staying locked back after the magazine is empty. I have used 20 and 30 round PMAGS and new Colt 30 round mags The bolt will lock back with a 30 PMAG without the can on. Just to clear up things, the bolt won't lock back when using the 20 round P-Mag and the 30 round Colt mag? It will lock back with the 30 round P-Mag? The first thing to check would insert an empty mag, pull back the charging handle and see if the bolt will lock back with out you pressing the bolt latch. This is to find out if the mags are actually pressing up on the latch which will cause it to lock back after the last round is fired. Have you done this? Did you do the one round test on all the mags? |
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Tag. My unknown mfg 11.5" 5.56 doesn't lock back on last shot most of the time, regardless of mag (20, 30, 40, pmag30). It usually has doublefeed and jam problems with my Colt 20rnd. Carbine buffer, 11.5" barrel had 5.5" Flash hider which I removed for easy SBR, pinned FS and A2 flash hider, no can. I have a few new 20rnd mags arriving on Friday, and an H buffer next week. Everything is well lubed and nothing appears to be binding. Hopefully next weekend I can give it a rip at the range and the H buffer will solve my problems. |
| I have done 1 and 2 round function test manually with snap caps in every type of magazine and the bolt locks back everytime and also with no rounds. The brass I would say is ejecting to about 3:00. And as I said earlier the rifle will function correctlly with a 30 PMAG without my HALO installed. |
| I don't have one but I may get a Full Auto group just to have one and see how that works. I'm going to tear it down in the next couple days and clean and check everything re-assemble lube the heck out of it and try it again. It's had around 300 rounds through it now. |
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So the bolt locks back normal when hand cycled so the bolt catch is working. This indicate that the bolt carrier isn't being cycled quite far enough by normal firing. So whatever the actual cause, the gun is not generating enough gas pressure to fully cycle the bolt consistantly. Some would suggest enlarging the gas port, but that is more of a last resort in my mind. I would start with the easy stuff. 1. make sure the gus is well cleaed and lubed. I would especially clean the gas tube since running a suppressor may cause more crud than normal to get in there. 2. Make the bolt easier to cycle. Try a standard buffer rather than the heavy buffer. The more mass the gun has to cycle the more gas it is going to need to do it. Also, as much as I like FA carriers, trying one of these or an H2 buffer only adds more mass, and is likely to make your problem worse. If all else fails, you may need to look at getting the gas port opened up a little. The problem could also be the opposite. Overgassing can cause the bolt to cycle too fast. It can actually go so fast that the mag pring doesn't have time to get the follower up fast enough to engage the bolt catch in time to do it's job. I think you would probably notice the excessive recoil and your brass would be getting tossed further than normal. I think this is less likely but is a possibility. If you notice your brass being thrown out forcefully, then an FA carrier and/or a H2 buffer may do the trick. |
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I don't have one but I may get a Full Auto group just to have one and see how that works. I'm going to tear it down in the next couple days and clean and check everything re-assemble lube the heck out of it and try it again. It's had around 300 rounds through it now. WTF you didn't even strip down the bolt and check the gas rings yet??? Make sure the gas rings are not damaged and check to see if the gap in each ring are not perfectly lined up, it can be rare but it does happen. |
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Quoted:
Quoted:
I don't have one but I may get a Full Auto group just to have one and see how that works. I'm going to tear it down in the next couple days and clean and check everything re-assemble lube the heck out of it and try it again. It's had around 300 rounds through it now. WTF you didn't even strip down the bolt and check the gas rings yet??? Make sure the gas rings are not damaged and check to see if the gap in each ring are not perfectly lined up, it can be rare but it does happen. That wouldn't make a difference and has been proven wrong. |
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m1dsniper,
i ran round and round with a similar with the same issue on one of my builds. you may want to pull the bolt catch and either replace or check for spec. on my build, suppressed the BCG would not lock back on empty mags and it did end up to be the mag catch was out of spec (not tall enough). fatkid |
| I appreciate all the suggestions here and think I'll start with the standard buffer and than maybe since it's not that big a deal to change the bolt latch. If that doesn't work than I may try a H2 and FA carrier before I would think about having the gas opened up. And yes the rifle has been torn down a couple times previously and the gas rings looked fine with no problems. |
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I don't think it's a matter of needing a lighter buffer. If your brass is ejecting at 3:00, you're good. If it starts flying forward of 3:00, which is what will happen with a lighter buffer, you're over-gassed.
I only use Pmags so I've never run into your problem, but I'd probably try another bolt catch to see if that's the issue. I have seen them be just barely too short, and I've also seen lowers' bolt catch location just barely too low. Obviously, try the easy fixes first(different BCG, different buffers, etc). |
| Back to the range today with a Noveske FA BCG and a standard weight carbine buffer and it worked like a champ 30 round PMAGS and a few 30 round Colts I have. It still doesn't like the four 20 round PMAGS I have kind of strange but works great with the 30s with the HALO and without the brass is landing about 2:00 from where I fire. It ate M193 and M855 with no problem. Thanks again to all here who helped me trouble shoot, great bunch of guys! |
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