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Posted: 7/15/2008 11:40:30 AM EDT
| Hey guys, my first posting a topic, but I've lurked awhile. I have a Bushmaster that I recently decided needed to be flattopped, as it was A2 style. So I bought a stripped Spike's Tactical flattop upper. The only problem is that I can't seem to get the barrel locking nut aligned so I can fit my gas tube in. Are there any tricks or ideas that anyone can help me with? I've tried starting the ring in several different locations but when I tighten it up, there is always a tooth sticking up and covering the gas tube opening of the upper receiver. Any help would be greatly appreciated. |
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How tight until it stops? Should take between 30 and 80 ft/lbs. to align. www.ar15.com/forums/topic.html?b=3&f=4&t=315921 |
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Repeat. It will eventually line up. Start at the minimum of 30 Ft-lbs and work up. Are you using a good moly lube? This really helps. And are you using correct upper receiver block and insert? Finally, are you bore sighting to make initial alignment of the sights better? Before final torque, set the rear sight to the middle position, then align the barrel to bore sight. You can get a good bit. Then, with the receiver clamped, lock the barrel with a second vise, like a drill press vise and barrel blocks. Lock the second vise to the bench with Bessy clamps and then tighten the barrel nut. Volia, no more canted FSBs! |
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Good, you have the blocks. To measure torque, the OCD folks will use a torque wrench but you have to consider the offset of the wrench center to the center of the 1/2" drive hole. On my wrench, this is about 1.75 inches. If my torque wrench is reading 100 Ft-lbs, and my wrench is 12" long, the actual wrench torque is indicated torque multiplied by (1.75 + 12)/12 IF and ONLY IF the lengths of the wrench extension and the wrench are in the same direction. Nut torque isn't all that precise...tight enough so it cannot be removed by hand without a wrench and then enough to align. Be sure to check sight alignment if you need to use more than 30 ft-lbs. |
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