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Posted: 7/26/2004 4:38:55 AM EDT
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Sirs, Have threaded and chambered barrels, 700's, 110's, Smith's so on. I have not worked on AR 15s as far as barreling goes. I have an AR to rebarrel, questions concern the barrel extension. How is the pin removed from the present barrel extension? Should I drill it out? Does the pin extend through the barrel extension into the barrel threads or a relief? Does this pin align with the hole in the barrel for the gas block or what is it's alignment? Any hints you'd like to give, or things to watch out for? I do have a complete machine shop. Lathes, mills, surface grinder stc. Thank you Haggard |
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Haggard - that is manufacturing level work. I'd be surprised if you found one other person in the build-it-yourself forum that has done it - let alone in this forum. You're best bet is to head over to the industry section and ask some of the 'smiths there like Kurt of Kurt's Kusotm. BTW Do you have a jig to align the gasport with the barrel extension and the indexing pin? |
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Typically, if you are machining a barrel from a blank, you would use a new barrel extension. But, if you want to use the old one, it should work fine. The pin does not go down into the threads on the barrel root, and there is no need to remove it to pull the barrel extension off. If it's a factory Colt installed extension, you will have to put about 300 pounds of torque on it to get it off. In the past, I have used a 2 foot breaker bar with a 6 foot piece of pipe on it, and then I about bust a friggin nut pulling on the pipe to break it loose. The first time I did it, it broke loose so violently, I almost did a back flip over the lathe. You will definately have put down your beer before you try this one. Cut the shank on the barrel root to .805", then thread it 16TPI with a single point cutter. Set the bolt face to barrel face clearance first at about .005-.006, then cut the chamber and headspace around .002 or so. When you go to punch the gas port at TDC, install your float tube or handguards first and select the port position so the block is nestled up close to the end of the handguards. You will find that float tubes from DPMS are about 1/4" longer than the ones from Olympic, so if you want your stuff to look right, cut the port after you verify the FFT length. There is plenty of leeway in the gas key so the depth of the tube is not an issue for functioning. I know, I have done about 400 of them. Also, you want your gas block to fit snug on the barrel, so you only have about .0005" room to get it dead nuts. Don't just cut it .935" or .750" and expect a good fit from your off-the-shelf gas block. You need to fit your gas block to the barrel when you cut it. Your block may be off a .001" either way. |
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TonyRamore, Thank you and the others for the answers. I have a shelin 224 barrel blank, a new barrel extension, came with no pin. I'm chambering this for a wildcat. All factory barrels I had a chance at were already chambered. My plan now is to turn the shank, thread, install the barrel extension, install barrel and headspace. I've got drill rod in many different sizes so making a pin should be no problem. I will use an adjustable reamer to fit the gasblock or make a D reamer. Some mentioned jigs. Corncerning the gas hole, if I get everything TDC or vertical, can I indicate off one side of the barrel , move to the center of the barrel and be OK?, or should I make a jig? This looks to be a relativly simple machining job, I've just never barreled an AR before. It looks like headspacing will be easier to hit than a 700 REM. This is a Colt barrel I wanted to remove the extension on. I think I'll use a 10 foot cheater pipe and a 20# hammer. What about adapting a barrel extension wrench to fit a 3/4" impact wrench? Since you've done 400, you know what you're talking about. Should I try to true the reciever (Olympic) like we do 700's, savages etc? Thank you Haggard |
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