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Posted: 1/9/2003 5:50:21 PM EST
I was thinking about taking an SP1 20' barrel, chopping it down to 14.5', rethreading it, and perm attaching a comp to make it legal. Can anybody give me some tips on this. Can I recrown the muzzle with a drill press like I think I can, rethreading is no problem, but where and what diameter should I drill the gas port?

Let me know,
J.D.
Link Posted: 1/9/2003 9:49:50 PM EST
Gas port location 6.875" from muzzle, port size from 0.063" to 0.078". What will you do with the old gas port? I imagine you could recrown the barrel with a solid setup and a good cutter.
Link Posted: 1/10/2003 2:42:31 AM EST
For shorty style handguards,the gas port should be around 178.5-180 mm from the barrel nut face of the the extension(DPMS and Oly dims).Gas port dims about right above.After chopping the barrel to length,a 7/32" piloted cutter,first to square the barrel and then perhaps an 11 degree cutter to finish.This can be done by hand or if great care taken,in a drill press.I suggest you check out Brownells catalogue over there although the first item may be loaned from a cylinder head reconditioners.
Link Posted: 1/10/2003 3:22:46 AM EST
Thanks for the info so far fella's. I was just going to use a drill press. I'm guessing the only bad thing that can happen is a failure to cycle the next round right. Once I shorten this barrel the old gas port will be gone, so no worries there. Does the port have to be on an exact 11 degree angle or will a few minutes off be okay? Sorry to ask so many questions, I'm just on a college student budget with too many tools on hand :)
Link Posted: 1/10/2003 4:56:44 AM EST
Use the dimensions given (178.5-180mm) for port location forward of the flange surface that the barrel nut touches. It will be located at TOP DEAD CENTER along with the index pin,,, see it on the barrel right now before you start.. The 11 degree refers to the crowning of the muzzle, though "facing" on a lathe will suffice. Just take the current sight base flange/ barrel shoulder dimensions as related to old barrel and simply move these dimensions rearward. For the gas port, start w/ .063. Place 1 round in the mag, chamber, fire, and see if recoil is good, and bolt-carrier locks open.. If no lock open, open port a hair and try again.
Link Posted: 1/10/2003 5:26:24 AM EST
Hey SBR, thanks for the clarifications. This is my first attempt at something like this. I didn't think it would be to hard, and so far doesn't seem like it will be, I'm just trying to get all my p's and q's in line before starting. Thanks again, J.D.
Link Posted: 1/10/2003 6:02:09 AM EST
About the old gas port, where is it located now? I'd be surprised if it comes off while chopping the barrel down to 14.5".
Link Posted: 1/10/2003 6:22:50 AM EST
I'll have to check again, I don't have the barrel here, but I'm almost positive that when I measured it, it's gonna come off. I'll let ya know, J.D.
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