01-02-2012, 01:54 AM
HI, first let me explain why I use green locktite to begin with. I shoot service rifles a lot, A2's and A3's which have a front sight tower and gas block combination. It is important to get the front sight tower perfectly plumb so that the rear sight has equal windage adjustment left and right of the no wind zero. Quality service rifle uppers have set screws that rotate the tower by pushing on flats milled into the barrel. You begin by adjusting the tower left and right until you have a no wind zero at 200 yards with the rear sight centered and then use the green loctite to bed the gas block to the barrel and also to set the set screws so no further movement is possible. You can use gravity but it really isn't necessary as the loctite will be drawn into any voids or gaps due to capillary action.
After achieving the no wind zero, I usually clamp the upper in a vise and apply a bead of the green loctite to the barrel to gas block interface, and the set screws, allow it to wick into the gaps and then wipe any excess away with an absorbent cloth. I should have mentioned that I cleaned the barrel tenon, gas block bore and set screws with alcohol before assembly or adjustment. Once the loctite has set up, about 8 hours I then apply a protective layer to prevent corrosion, CLP or similar.
When I was at the NRA school of gunsmithing, some of the students used blue loctite on the barrel nut threads, but for reasons I never got to the bottom of they had to remove the barrels on some of them which required a torch and much outgassing. I saw no advantage to this compared to anti seize which came apart easily if needed.
We went to the NRA Whittington center and shot all the uppers we built at ranges up to 1,000 yards. The uppers built with loctite on the threads all shot worse than those with anti seize but I wouldn't attribute too much science to that as their were barrel quality issues mixed in with the results.
We took a lot of time examining all the barrels with a Hawkeye bore scope hooked up to a big screen TV so everyone could see the issues. After examining a few dozen barrels it doesn't take a rocket scientist to migrate from Shaw's to Kreiger's.
My personal belief is that a lot of hocus pocus is used to explain away poor performance from poorer quality barrels.
I'm on my fourth Kreiger barrel on my service rifle now and all of them have delivered less than .5 MOA with vanilla flavored upper receivers without tuning loads for them.
So to fully answer your questions, I think bedding the gas block is important, not always but in some instances where bad harmonics play. I don't think squaring the receiver face or tight fitting barrel extensions are important. It is important to use enough toque to get the barrel nut firmly engaged, and do so by backing off and retightening a couple of times. And I do think it is important to make sure the gas tube is centered and not rubbing on one side or the other of the passage way through the reciever.
Bob
After achieving the no wind zero, I usually clamp the upper in a vise and apply a bead of the green loctite to the barrel to gas block interface, and the set screws, allow it to wick into the gaps and then wipe any excess away with an absorbent cloth. I should have mentioned that I cleaned the barrel tenon, gas block bore and set screws with alcohol before assembly or adjustment. Once the loctite has set up, about 8 hours I then apply a protective layer to prevent corrosion, CLP or similar.
When I was at the NRA school of gunsmithing, some of the students used blue loctite on the barrel nut threads, but for reasons I never got to the bottom of they had to remove the barrels on some of them which required a torch and much outgassing. I saw no advantage to this compared to anti seize which came apart easily if needed.
We went to the NRA Whittington center and shot all the uppers we built at ranges up to 1,000 yards. The uppers built with loctite on the threads all shot worse than those with anti seize but I wouldn't attribute too much science to that as their were barrel quality issues mixed in with the results.
We took a lot of time examining all the barrels with a Hawkeye bore scope hooked up to a big screen TV so everyone could see the issues. After examining a few dozen barrels it doesn't take a rocket scientist to migrate from Shaw's to Kreiger's.
My personal belief is that a lot of hocus pocus is used to explain away poor performance from poorer quality barrels.
I'm on my fourth Kreiger barrel on my service rifle now and all of them have delivered less than .5 MOA with vanilla flavored upper receivers without tuning loads for them.
So to fully answer your questions, I think bedding the gas block is important, not always but in some instances where bad harmonics play. I don't think squaring the receiver face or tight fitting barrel extensions are important. It is important to use enough toque to get the barrel nut firmly engaged, and do so by backing off and retightening a couple of times. And I do think it is important to make sure the gas tube is centered and not rubbing on one side or the other of the passage way through the reciever.
Bob