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Posted: 9/19/2006 12:13:25 PM EDT
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Here's the deal. About a week ago I took my new carbine to the range. I notice right off that it would not hold the bolt back on an empty mag. Then after around 40 or so roounds it stopped running at all. Checked the bcg and it was dry. I had oiled it just before going to the range. We packed up and came home. Got home that day and cleaned everything up, checked the gas tube and all other parts. No obvious problems found. I'm thinking at this point that it's new and I ran it dry. Fast foward to today and I go back to the range with an assortment of ammo some spare parts and all my cleaning and oiling supplies. Okay I get to the range and put one cartridge in the mag, shoot it and the bolt closes on the empty chamber. Tried this five times with Winchester Q3131, same results each time. So I try some Federal AE and the bolt locks back, I'm thinking now it just finicky about ammo, this works for the five times test also. So I try some Quat. milsurp and it either has a failure to eject the spent case or closes on an open chamber. When the Quat did eject it would not pick up another round. So by now I'm thinking stick to the AE for now but about half a mag and it's not picking up the next round after ejection  . Starting to get bothered now so I pull the bolt and it was still well lubed. I decide to try another buffer and spring that I took with me.Well it did not like the other buffer setup at all. So after a few minutes grumbling a few choice words to myself I decide to try the well used Model 1 sales bcg that I have in my spare parts. Lubed up the spart bcg and put her in there. Well now she runs like a dream, perfect will all ammo I had with me. Now this is the question, the bolt that I took out was an almost new Colt half circle bolt and the Model 1 was a full circle bolt. I put them on my scales and there is about 2 grams of difference in weight. Did that 2 grams make all that much difference or does the Colt bcg have a problem? This is the first half circle carrier I have owned and it looks great inside and out. The rifle is a superlite 16 BM barrel, A1 upper, RRA lower and 2 position aluminum stock. Am I just stuck with a bcg that going to be a problem in other guns.  Thanks in advance for any advice. Elvis |
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With one working B/C and one not working B/C, the troubleshooting is going to be real easy on figuring out the problem, and resolving it. Since a B/C is a few parts assembled to make one unit, this allows to trouble shoot each part at a time. Start off with pulling the bolt and cam pin from the M-1 B/C, and installing them in the Colt (non-working B/C) and shoot the rifle for a 10 rounds. If the Colt B/C works with the M-1 parts (bolt and cam), then pull just the M-1 bolt out of the Colt carrier, and install the Colt bolt I and test for 10 rounds (leave the M-1 cam in the Colt B/C for now and retest. If everything is good so far, put the Colt cam back in with the other colt parts and retest. Now if the Colt carrier alone is a problem, then you need to first tilt test the colt carrier (just the carrier) in the rifle. This done by shot gunning the upper open, pulling back on the carrier in the receiver, and with the muzzle angled downwards at 45* let go of the carrier and see if it slips forward on it’s own. If the carrier will not slip down on it’s own weight, then chances are the upper receiver track is on the tight side, and you may need to lap the bearing sides of the key to prevent it from binding down the upper receiver track. If the carrier slips freely, install the rest of the colt parts, and re-slip test. If every thing is good so far and nothing is binding during the slip test, then its time to pull the key and reinstall it (I’ll go into more detail later if the key leaking is the problem. If the next step of adding the bolt alone to the colt carrier causes the problem, then the Colt bolt against the barrel it’s self too tight of headspace, and the bolt it’s self is just not going to work with the Bushmaster barrel. Note: The bolt may head space in another barrel fine, so don’t panic yet thinking that you have a spare bolt you can never use. As for the last step of adding the Colt cam, if the Colt cam alone is causing the problems in the Colt B/C, then you need to lap the bearing edges of the cam, and check the cam slot in the carrier (forward edge). The problem really goes back to a tight upper receiver key channel itself; that of when the B/C unlocks and moves in the upper receiver, the key and the cam are the only two items tracking. What may be happening is the that the cam in not going all the way forward in the carrier slot to allow the cam to get inline with the key, and it’s bind city. Also, mic the key bearing sides against the cam bearing sides. You want to make sure that both are the same width, and neither of them has a corner that is protruding and could be catching on the upper receiver key channel. To conclude it’s just a matter of testing each part one at a time to find the flaw in the system. Also, don’t be surprised to find that with the M-1 B/C having run in the rifle for a few hundred rounds to loosen up the upper receiver key track, that the Colt B/C just magically works in the rifle down the road/through the tests, even without doing a dam thing to it. |
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