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Posted: 11/23/2007 11:17:54 AM EDT
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Guys, put together a 7.62x39 upper for my AR15. The upper receive is Stag/CMT, the barrel is DPMS heavy 20 inch. The carrier is a Colt and the bolt is a CMT. Additional information: I also tried a new Colt 5.56 bolt. Okay here's the problem. Running the carrier/bolt assembly into the upper and the bolt stops solid as soon as it touched the barrel extension. If you give it a tap with your hand on the back of the carrier or if it's assembled on the lower, the recoil spring will seat it fully. The first few times it was pretty hard to open. I had to put a glove on and yank the charging handle pretty hard and it come open. I noticed when opening it slowly the bolt lugs will come about 1/2 to 3/4 the way out of the barrel extension lugs, then gets tight, a yank and she's out. As I said I tried the CMT 7.62 bolt and a new Colt 5.56 bolt....no change, both feel the same. Being the Colt bolt is new and the barrel extension is new, there are no marks where it might be binding. So I lubes up the lugs with some STP assembled the rifle and worked the bolt back and forth. The more I worked it, the easier it has gotten. I haven't fired it yet as I don't have a gas tube. They sent me a carbine length tube and I need a rifle length. So what's this sound like? Little misalignment? Thanks for whatever input I get. Joe |
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Shotgun the upper open and take a look at the center section of the feed ramps against the bottom front lug. If the feed ramp center is centered on the front take down lug of the upper, it's time to just shot the piss out of the upper and allow everything to mate in like normal. Also, when you do install the new gas tube, confirm its alignment via just the carrier without the bolt alone feed down the upper track. The carrier key will have a slight resistance when the tube loads, but the tube should not be flexing a great deal as it loads. If the tube does not enter the key cleanly, then you will need to adjust the tube to correctly index above the barrel. Lastly, before you even take the rifle out for the first time, check the firing pin protrusion out the bolt face. You want it to be in the .037 range, and not the .032 that is normal for the 223. If you find that the FP protrusion is short, the quick way is to just set back the stop collar on the FP verses having to shorten the tail of the bolt to achieve such. |
Dano, thanks. I was going to take a look at it this morning after I get back from shopping. I paid attention when I installed the barrel into the upper making sure that it wasn't a sloppy fit and that the indexing pin was tight in it's slot with no side play, which it was fine. The front sight was straight up also. I was thinking last night that maybe when torquing the barrel that it might just be turned a wee bit in the receiver misaligning the bolt entering. I'll check what you said and report back asap. Thanks Joe |
Dano, Last night laying in bed I was thinking whether that barrel was canted some. Well I went and checked after reading your post and by God it is and it's in the direction of the barrel nut torque. So I'll pull it apart and see how much slack is in that extension slot and then file and peen the necessary areas to align it. Yes I have grease on the threads and face of the barrel extension the barrel nut torques against. Thanks for your help, I appreciate it. Ring this one up, you got it right!! Joe |
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Dano, Took the barrel off and instead of peening anything I made a shim to fit between the barrel extension indexing stud. That did it. This time when I torqued up the nut I not only had the receiver in a receiver block, I held the barrel too. This way for sure the only thing that was going to turn was the barrel nut. Bolt slips in fine and I put a gas tube in it and she run fine. Again Thanks Joe |
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