I have a Colt MT6551 (A2 style barrel)
that I bought new in 2001. There are probably
3000 rounds shot through it since then.

The problem I noticed is that the barrel is loose where it screws into the receiver.
You can rotate it and hear where index pin
fits in the receiver.

Has anyone heard of this and what's the cure ?

Give Colt a call, have them fix it.

[url=http://www.colt.com/CMCI/custserv.asp]Colt customer service[/url]

[url=http://www.colt.com/CMCI/dealerlocator.asp]Colt Dealer locator[/url]

Unless you want to DIY.

What's the fix...take the gas tube out and tighten it another notch ?

If that's the case I could do it myself.

Have you heard of this before, is it common
for high round count AR's ?

No, but it's common for Colt's made during that period. [rolleyes] Something about union negotiations.

Yeah, if you've got the tools (vice, blocks, wrench, pin punch) just pull off the handguards, remove the gas tube and back the nut off. Check that the threads and nut (esp the inside of the flange) are greased (MoS2) then work the nut onto the receiver. You can use the gas tube as an alignment gage if you have a good eye.

While you have the gas tube out check the carrier key end of it and make sure it isn't worn away.

Once you think the teeth on the nut are aligned with the gas tube hole in the upper install the gas tube. Slide the gas tube into the upper and make sure the tube sits centered in the upper and on the barrel. A check is it to run the tube into the upper further than normal so that it clears the rear of the FSB and points at the hole in the rear of the FSB. When the nut is correclty indexed  the tube should point directly at the hole in the FSB. Harder to described than to do.

Anyway, once you get the gas tube reinstalled check the alignment by stripping the bolt out off the carrier and sliding just the carrier in and out of the upper by hand. You shouldn't feel any binding of the carrier key on the gas tube.

I headed down south to audit a rifle class and fix anything that breaks so if you have any more Q's you'll have to take what you can get from the others. [^]

Thanks for the help Tweak.

geez, jus' as soon as I kin git outa the outhouse, i'm gonna git me one 'o them thar hr fifteeny guns whut makes a boom an see iffin I can take 'er apart.
When i am dun, I will fix yore gun right up real perty!  But only if ya say perty pleeeeze.
Now where's thet there hammer whut I used on the horse shoe?
[banana]

royce,

If that's how you want to take my post then that's fine.