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Posted: 2/13/2011 6:15:24 PM EDT
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I put together a A2 upper with a 20" colt 1/7 5.56 barrel with a fixed front sight base last week and took it out to shoot today. Well it's in single fire mode only right now. The bolt doesn't even slide back after the round is fired. I fired 10 rounds this way before putting it down and picking up my ever faithful BCM.
I have lubed it well with mil-com. So it shouldn't be that it's not lubed enough. I checked the gas tube to make sure it was good. I can blow air through it easily when it's out of the fsb and in my hands. I checked the fsb to make sure that gas could get from the barrel to the gas tube with a flash light. I can very clearly see the light inside the barrel when shining it through the fsb. The ammo being used was remington umc. And I have never had a problem with it cycling anything else. The bcg is a Colt. I for the life of me cannot figure out why the bolt is not even attempting to slide back. It's probably something simple and I am just not looking or thinking in the right place. Any ideas would be awesome. |
| Try switching BCG out of the BCM for a couple of shots. That should give you a better idea of what's happening. Probably cure problem then switch out bolt for a couple of shots. Narrow down to carrier or bolt. Carriers especially Colt are not known for problems. I'm gonna assume everything moves nice and free in the upper when lower is removed. |
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i agree... try and switch out parts to see if you can narrow it down.
Another thing might be that you don't have the gas block lined up correctly... you have it partially aligned so you can see the light.. but not lined up enough to transfer the amount of gas needed to cycle. there is that old story about gas rings having to be staggered so there is a seal... but i have heard conflicting reports on whether or not that is true... easily checked though. |
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Another thing might be that you don't have the gas block lined up correctly... you have it partially aligned so you can see the light.. but not lined up enough to transfer the amount of gas needed to cycle.
Got any pics. Is that a surplus Colt A-2 barrel? If so hard to believe a problem with FSB after many years of military service. Lot of assumption here on what you actually have. Sounds like you built a surplus A-2 clone which should be GTG. Where did you get the BCG? Try switching the BCG first. I'd have done that after the first shot failed to extract but I've never had a problem with cycling either. I also take two rifles with me shooting, a spare bolt and firing pin just in case, but haven't needed yet. It's a 70 mi trip for me and I'm gonna do some shooting. |
| I got the barrel from landman with the fsb being pinned, it not a surplus used barrel. It's very more than likely just been test fired then put up for safe keeping.. I will try the swapping bolts. If that works then I have a extra set of gas rings I could try replacing. It does move freely when it's off of the lower also. |
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Can you blow air through the gas tube (use a piece of tubing slid over the gas tube) when it is installed? Is the carrier key secure & clear? Yes, it's in the first post. Sorry, I misunderstood when you said it is clear when removed from the system and holding in you hand (like a straw). |
| I tried it with a strw like you said and I could feel air coming out of the end of the barrel. I will hopefulle be able to shoot again this weekend and if I do I will take it with me and a few tools to work on it if need be. I am quite baffled as to the problem. The gas tube didn't have any dark markings on it like it would if the fsb were leaking either. |
| I took it back out today. And low and behold my bcg is sliding back,. it's just not picking up the next shell from the mag. I changed mags and still no go. So I then changed lowers and it ran fine. Next I took the colt bcg out of the A2 and put in my BCM bcg from my other rifle. And it ran great. Therefore it has to be something wrong with the bolt. I am heading out to the basement now to check it out. |
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yep. I just can't figure out whats wrong with the bolt. It is sliding back so I know the gas rings are working. They are not broke are even look worn. It's just not picking up the next round when it slides forward. Mic the lugs and bolt recess channel, and tail width, and then also confirm that the gas section bugle (straight to flair) of the bolt tale is milled correctly as well. |
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Is it possible the bolt is dragging on the hammer, or the hammer/hammer spring is out of spec? Best guess, the bolt lugs depth to the face recess of the bolt is out of spec, creating too tight of a head space, and causing the fail to full stroke. I saw this a few years back when some barrel where head spaced too tight, and no mater what, then would short stroke. But is also could be the tail of the bolt to the carrier pass through for it has too much clearance, and you can get way to much blow by through the back end of the carrier to cause short stroking as well. Since the round is going off, best to guess that the hammer and it's stroke are fine since there is enough force to set the primer off. |
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