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Posted: 8/26/2006 9:01:59 PM EDT
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So, I have finally taken the plunge and decided to assemble an upper. I've done a few lowers and found it much less challenging than expected. Here is my question: How best to install an A2 FH? I will be using a crush washer and putting it on a 16" Superlight barrel. Should I put it on hand tight, then install the barrel on the upper, then index/tighten FH while the whole works is clamped in the vice? Do I put anti-seize on the threads for the FH? Help a noob out! Thanks! |
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Use a barrel vise to index the flash hider. Read this tread: Barrel vise? Pay special attention to what FALARAK says, as it is good advice & is common sense not to put any more strain on the barrel index pin or the slot on the receiver than needed. If you bend the pin or stretch the slot on the receiver your FSB will more than likely be canted & you will lose accuracy. If you don't want to spend the money on a barrel vise, get a peice of hard wood (I used Oak) about 10" long & router a V-groove into it, then cut it in half. Instand barrel vise! 
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This is taken from the ARMY manual that you can download right here. Recessed washer does not require torqueing 15B. Assemble compensator to the barrel using recessed washer (12991533)(fig C-6, item 5) with the large diameter of the recessed washer forward toward the compensator and the small diameter rearward toward the barrel. Tighten the compensator hand tight and then tighten a minimum of 90 degrees but no more than 460 degrees to the center of the middle slot. If you look it up it is on page 3-44. Just make sure that out of the 5 slot that number 3, center slot, ends up top dead center no mater where the wrench cuts are at. Pat 
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I dont put anything on the threads. Never had one lock up. Sometimes it only take s asmall amount of torque to crush the washer. Lately, a lot of crush washers are around that wont crush (easily) and take a lot of torque to index them. Honestly... I shouldnt admit this... but if working on a barrel with a pinned FSB, I usually just vise the FSB between two blocks of wood and tighten her down. Always install your barrel first. Muzzle device is last. The "right" way is to clamp the barrel in vise blocks. You can install a flash hider using the action block... but if you have to torque it much at all, thats not good, for the same reason installing a barrel nut with vise blocks isnt - it puts all the streed on the indexing pin against the upper receiver slot. Some people will wrap the barrel in a little leather, and install the FH that way. The key with a crush washer is to start it crusing, then index it so the enclosed part is to the bottom. If you get one that doesnt want to crush... you can take it out and pound it with a hammer on a wood block to start it deforming... sometimes that helps. If to index it... it gets really tight - then go past the correct index slightly... so that it indexes with a lighter amount of torque. Too tight on the muzzle device can impact accuracy to the purist. |
That's my method too. Two pieces of 1x3" pine wood in a vise on each side of the FSB. The soft wood gives enough to smoosh around the FSB without marring it, and the wood pieces are strong enough to let you torque that FH down tight enough to crush the washer. Mine was a mutha to crush. My YHM Phantom 5C2 ended up hand tight JUST past the spot I wanted it at, with the top slot at about 1 o'clock - d'oh! To crush it without over-torquing the barrel, I just tightened, then loosened it and repeated until the washer was crushed enough to tighten it one last time the rest of the way to having the top slot at 12 o'clock. I read how to do that on here (BIY forum) in other posts. |
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Well, thanks alot guys! Got home and the rest of my pieces parts had arrived, so I put it all together. Went well, and, like the lower, was less challenging than I had imagined. Thanks for the tips! This was my first complete assembly from parts. And I guess it wasn't even a complete assembly as the Bushy BBL aready had the FSB and extension in place, but you get my point...  If I could stop spending money on gun stuff, I might actually be able to afford a camera so I could post pics! 
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