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Posted: 1/6/2005 7:18:18 AM EDT
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With set screws. quite sure this have not been moved, there is some rather deep notches where the screws hit the barrel, so I get a good feel, when they are right, and the rifle worked perfectly before I cut the barrel, and the part of the barrel where the gas block sits, have not been altered. Tried to insert a cartridge in the chamber and fire, today, after I had replaced the gas rings with new ones,it would not lock back. I then went true a 30 round mag, and it ejected all the spent cases, but did not lock back on the last. Then tryed with just one cartridge, in 10 different new mil spec mags, did not lock!! |
| not so much worried that the GB has moved as it wasn't aligned properly to begin with. pull it off and make sure that the hole in the underside aligns with the hole in the gas tube (use the proper sized drill bit) and then double check the alignment of the GB with the gas port. |
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Quoted: I had my DPMS varmint barrel 20" cut down to 18,5" and the barrel turned down to about .875 overall, exept for where the gas block sits. I also had a JP kompensator fitted. This was about to work fine the gunsmith stated before cutting. Now I have problems with mostly all military and comersial ammo. My home made stuff works ok, as long as I use rather slow burning powder (W-748) I'm think the gas port on the barrel have to be opened some, but how mutch? I do not trust the gunsmith to find this out!  your 20" bull barrel should have a.093 gas port hole, DPMS makes a dissy style barrel cutting a 20"Hbar back to 16" and using the original 20" gas port location.The port in that barrel is .106, Iwould think if you started inbetween these ports sizes [about .099] you would have a good starting point. 
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If it was my rifle, I wouldn't touch/oversize the gas port until I was sure that the gas block was installed indexed with the gas port (not the upper receiver) and the barrel extension/barrel was installed in the upper receiver that the bolt lugs were true with the barrel extension lugs (lock and unlock). Over sizing the gas port more than needed is a bad one-way street with no U turns. Get the port too large, and the action opens too fast, with the accuracy of the barrel/rifle being lost (you end up installing a adjustable gas tube to slow the action back down). The best advice I can give you is to check everything else out before attacking the gas port. When it comes to gas pulse to the B/C, you only want just enough to cycle the system if accuracy is one of the top items on the rifle/rig. |
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