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Posted: 6/5/2009 8:35:17 PM EDT
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ARF members:
I need to remove a barrel extension and replace it with an M4-type with feedramp cuts. Do I simply buy the extension and tool from Brownells, clamp the barrel in a vise and take it off? Or, is it torqued to 150+ ft. lbs and I'll more than likely damage something? Also, why don't the replacement barrel extensions come with the alignment pin? Any and all help is greatly appreciated! Thanks! 'wolfe |
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You're most likely not going to be able to get a replacement extension to index properly, especially if you have to get the feedramps lined up.
Do you really need the feedramps? Most setups work fine without them. The only reason you would need them if if your upper has the cuts and your extension does not. Or if you plan on shooting FA. If you do, your best bet would be to send your barrel to someone that will cut them for you. |
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http://www.ar15.com/forums/topic.html?b=3&f=4&t=446061
Just a day and a half old... http://www.ar15.com/forums/topic.html?b=3&f=4&t=434170 Quoted:
Any and all help is greatly appreciated! Completely disabuse yourself of any idea of changing barrel extensions. |
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When a production barrel is made, the extension is screwed on and the indexing pin inserted. After that it is chucked into a jig and the gas port is drilled with the jig indexing off the extension. Since the threads on all parts are not timed, that means unscrewing and replacing the barrel extension will destroy your barrel. Even professional machinists on this site say they would never attempt it in their wildest dreams.
The barrel extension sold by companies are for producing custom barrels where you basically go through all the steps described above. Unless its a virgin barrel you are basically out of luck. If your not happy with your upper, sell what you have and buy new. If you ask many members here though, standard feed ramps have been run on thousands of rifles for millions of round without a hiccup. ETA the chamber is also reamed once the extension is torqued on, meaning if by the grace of God you did get it to line up remotely close, the chances of it passing a headspace check are slim to none. |
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I managed to obtain some slightly-used barrels from my department, sans the barrel extensions. I sent them to Dwayne at DEZ Arms, and he installed new M4 barrel extensions for me. However, as other posters mentioned, the chamber needed to be re-reamed & headspace verified, a new alignment pin drilled & installed, AND new gas ports drilled so that they were properly indexed with the alignment pins. Dwayne told me to make sure I use a 2-piece gas block, to ensure a nice tight fit and minimize gas leaks around the block. It can be done, but you're better off buying a barrel that already has the M4 extension already installed & indexed. |
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