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Page AR-15 » Build It Yourself
AR Sponsor: bravocompany
Posted: 4/18/2007 1:39:25 PM EDT
A recent build (that I haven't had a chance to get out to the range with) has what appears to be a fairly tight fit between the gas tube and the gas key.  I had to use a some force to get the bolt to close the first time.  It has loosened up slightly, but when I use the charging handle to open the bolt, it sticks and requires more force than usual to get the bolt to move rearward.

I'm a little concerned about gas pressure the first time I take it out.  Do I have to worry about anything safety related if there is a delay in the bolt opening (ie, will it KB?), or any concerns with the way the rifle will function?  Is there any remedy before I take the gun out the first time?

CMT Upper
Bushmaster Barrel
Carbine Gas Tube
CMT / Denny's Superduty M16 Bolt Carrier Group

Link Posted: 4/18/2007 2:48:22 PM EDT
Remove the bolt and try pushing just the carrier home. If it's still tight, then you likely have a tight gas tube/key. If not, then I'd wager just the gas rings need a little breaking in.

I had a Colt with a very tight gas tube/key. No problems.
Link Posted: 4/18/2007 2:59:47 PM EDT
You should be able to slide the BCG into the upper with light fingertip pressure - there should be no increase in resistance as the key encounters the gas tube.  You're likely to have FTFs since the bolt probably won't close, but there shouldn't be a KB.  Either the key or tube is out of spec or there's some crud interfering.  You can clean the outside of the tube and the inside of key with a cotton swab wet with CLP or your solvent of choice.  If you still have problems, measure the diameter of the mushroom on the end of the gas tube; it should be 0.186" IIRC, the same as the full-diameter portion of the tube.  If the tube is the right diameter, the problem is the key.   If yoou don't want to return the offending part, you can reduce the OD of the mushroom with emery paper (work carefully - you want it to be round, not elliptical) or open the ID of the key with a drill bit, but the vendor certainly won't repair/replace/refund if you've attempted to modify it yourself..  
Link Posted: 4/18/2007 4:48:59 PM EDT
Also make darn sure the gas tube is centered in the upper and that the barrel nut is not pushing it to one side. This will sometimes happen if the barrel nut is turned until the gas tube JUST fits in, instead of completely aligning the tube hole.
Link Posted: 4/18/2007 5:45:56 PM EDT
Ok, thanks for the replies.  The bolt will close completely if I release the bolt catch so as long as I'm not going to blow my face off I'll just take it out and see if it will cycle.  If so I'm sure it will break in.
Page AR-15 » Build It Yourself
AR Sponsor: bravocompany
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