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Old January 8, 2009, 12:56 AM   #1
2amencw
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Join Date: December 3, 2008
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ar headspacing

just got a cmmg barrel from numrich. it did not have the barrel ext. on it so i got an ext from blackthorne.when i assemble it and tighten everything the gas port does not align. also in this position the lugs can not engage. if i back it out untill the lugs engage or the port is in alignment the barrel is very wobbly. obviously i need a headspace gauge, but what about the port and wobble problem? is it feasable to shim the barrel with very a precise washer or barrel shim, and if the gas port wont align can i plug the old port by tapping and putting a blind screw in the hole and then reboring a new one? help!!! Thanks cw
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Old January 10, 2009, 03:13 AM   #2
T. O'Heir
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"...The answer to your dilema is long winded..." Not really. A barrel for any rifle has to be installed properly and adjusted for headspace. Barrels are not drop in parts. Doesn't matter where it came from or who made it. You need a smithy to install your new barrel.
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Old January 10, 2009, 11:46 AM   #3
2amencw
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ar headspace

Thank you for the assistance. I bought the barrel based on the illustration which showed it to be complete with ext. foolish me. I do understand the process involved in setting initial headspace on a virgin barrel and have done it for several pieces. This one is creating a challenge because it turned out to be a take off piece. I have several issues that i have to bring into alignment simultaneously. complicated but doable. I am not in a rush at the moment so I will seek the guidance of the specialists that you recommended. I was hoping to make this a superlow cost build but I see that fading into an educational build. Sometimes that is even more valuable. Thanks CW
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Old January 11, 2009, 08:34 PM   #4
2amencw
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ar head space

sat down to watch a movie last night(eagle-eye) and got my pile of parts out. took some peel type shim material i have in an 8x8 sheet. made some 2in squares and cut them into a ring. added them one at a time, they are about 5 thousanths thick. added four and got the barrel to align hand tight. i am going to add 1 more and torque the assy. if successful i think this would solve the problem. I am later going to have a friend machine a solid shim ring to use for the permanent mount. does it sound like i am in the right ballpark? thanks for the help. cw
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Old January 11, 2009, 10:57 PM   #5
sadsack
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2amencw: You can get into a world of hurt if your not careful. I wouldn't recommend adding shims at all, better to do the job right and be safe.
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Old January 12, 2009, 02:03 AM   #6
2amencw
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ar headspace

I understand the issues involved and i wouldnt do anything dangerous. Thank you for your input. cw
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Old January 12, 2009, 10:44 AM   #7
Alleykat
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Quote:
"...The answer to your dilema is long winded..." Not really. A barrel for any rifle has to be installed properly and adjusted for headspace. Barrels are not drop in parts. Doesn't matter where it came from or who made it. You need a smithy to install your new barrel.
Not exactly an accurate statement...as far as ARs are concerned. I'd opine that most AR barrels come with the barrel extension installed and headspaced. With such barrels, it's pretty simple to just "drop in" the barrel and apply proper torque to the barrel nut. When buying an AR barrel, be sure and ascertain from the supplier whether the barrel extension is installed and that the barrel is headspaced.
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Old January 14, 2009, 09:54 PM   #8
Harry Bonar
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AR

AlleyKat;
Good call!
Harry B.
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