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Posted: 3/29/2007 5:10:44 PM EDT
| could someone mic a bolt at the "belt"? I've got one here that won't fit into either my (suspected Colt) slickside carrier or my FN M16 carrier. |
I just happen to have both my bolt and calipers at my desk... Belt just behind the extractor pinhole - .528" Minor dia. of bolt - .512" Flanges either side of the rings - .487" OD of rings themselves - .503" ID of carrier bore - .531" |
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Thanks! This bolt measures .531 at the belt, .515 minor diameter; the carrier bore is .533; so why doesn't it fit? hmmmmmm..... It appears the flanges on either side of the rings are unable to pass the step in the back of the carrier bore where the gas port is. The flanges measure .491 Looks like this (SEI) bolt is out of spec. I'll see if I can get another bolt to confirm. |
| Hmm, interesting. I don't have a bore mic to check the rear section of the bolt carrier bore. .002" is a hair on the tight side, but shouldn't be that much of a problem. If you can get ahold of a bore mic you could take the rings off and polish down the flanges a hair. Best bet would probably be a split ring around the bolt body to hold 'em true in a lathe chuck and some emery cloth. Or stick the small end of the bolt in a drill chuck. |
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Ah, therein lies the rub. This is a SEI bolt, it be hard chrome plated. Whats worse, it arrived from Brownells less the gas rings  They have sent a McFarland ring to make up for it, but if the damn thing doesn't fit my carrier(s), fat lot of good that will do eh? Meantime I ordered a complete CMT BCG from Denny. When it arrives I will see what fits what and who will be hearing about it 
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Bolt tail is just under 0.250" and the bore in the carrier should be right at 0.250" This is the secondary gas sealing area on the bolt/carrier fit so the clearance should be absolutely minimal. Most dimensions on AR's are nice round numbers so that 0.531" measurement is probably 17/32" nominal and 0.531" being right where it should be. |
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