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I bought a used Colt 20" HBAR (MT6601). Its in very good shape from what i can tell. The only thing is when I cleaned it I noticed the bolt doesn't slide too easily in and out of the bolt carrier. In other words, when you hold the assembled bolt carrier in your hand and shake it, the bolt doesnt easily extend. It will if you shake it but not like I see them freely move in some of the cleaning videos I've seen. The extractor pin is properly in place as well as cam pin etc. The friction seems to be on the slightly raised ring on the bolt rubbing against the inside of the carrier. I know w knew guns there can be a "break in" period where this happens but this is a used gun. Haven't shot it yet and the guy I bought it from is out of the country for some time so I can't ask him. Any thoughts?
 

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It shouldn't be so loose as to extend just by shaking it. Sounds like it is about right. As long as it closes and locks in normal operation I would be too concerned about it. It has three gas rings on the tail end of it so it's not going to slide real easy.
 

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Fun And Easy Safety And Wear Checks ...

Check your gas rings for breaks or big gaps or missing rings. They do not need to be spaced one third around. Remove the cam pin and see how tight the bolt head slides in the carrier without the cam pin installed.

Eye ball the cam pin carefully for rings around it from premature wear with the carrier. There should ideally be none. A little bit is considered normal. Check the bolt body for cracks/chips around the cam pin hole and strongly bend the bolt to look for fracture cracks.

No need to pull the bolt head and check it for scratches from the key screws. Check inside the chrome lined portion of the carrier for more scratches. See if the firing pin slides free. Make sure the extractor is not too far outboard. Check for chips around the cam pin hole.

FWIW; "flinging" out the assembled carrier group to extend the bolt head is not a good idea. Closet commando stuff. Sometimes you really do not want to make quick jerky motions. Slowly extend the bolt head with both hands. Quiet and slow.

HB of CJ (old coot) hundreds of AR15 builds. Now you may know more. Just passing it forward. Respectfully. The AR15 likes lots of oil in and on the carrier group. Any excess will just quickly be flung into your eyes if you are a Lefty. Yikes! :)
 

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Checking gas rings and bolt fit:

1. Extend bolt in forward position

2. Set on flat surface bolt face down

3. If the carrier slides back over the bolt under its own wait replace gad rings.

Colt Armorer
 

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Easy Gas Rings And Carrier Key Alignment/Wear Checks ...

Gas rings may last 20,000 rounds. The longer they go, the better they have lapped in. Kinda like piston rings. A well broken in AR15 rifle carrier group/gas ring "friction feel" may feel slick and easy, but the rings are just doing their job correctly. No need to change rings just because gravity drops the carrier down with the group inverted on the bolt head.

I believe the "Colt" test was designed to sell gas rings? With high mileage rifles, if the rings are that far gone, then the carrier channel is also past spec and both will have to be changed out. This kinda dove ties with exterior carrier/upper receiver wear. The service life tends to be the same. But ... with broken/missing rings, change them.

The fun easy carrier key alignment test is fun and easy. Unload rifle. Separate. Strip out the bolt group. Invert the rifle muzzle down and drop the carrier with key down over the gas tube. The carrier and key should plop, (good word) down without touching the gas tube one little bit. No friction what so every. This can be tricky doing builds with loose parts.

Without seeing and handling the Rifle, it is difficult to state a problem or cause. There may not be any. Tolerances vary. Certain combinations of parts will result in different "feels" Actually, a "tight feeling" carrier group may be better. More room for precision and longer wear. Colt builds great stuff that may be tight. Hope this helps some.

HB of CJ (old coot) hundreds of AR15 builds and uncounted assisted with others thousands of M16 rebuilds. Long ago and far away. Now I want a left handed AR10 God help me. This stuff is so fun. Lefty AR10 uppers and carrier groups in the works, so my spies tell me. It would be so much fun to re enter the fun and madness. :)
 
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