I am working on installing a muzzle brake (Precision armament m4-72) on my heavy barrel 308. I chose to get the PA accu-washer shim set to time the brake. I chose the one I thought was correct, but when tightening down the brake, I could not get it to index properly. Didn't use a torque wrench, but I suspect it got a bit tighter than the recommender 20-30ftlbs. So, now I'm going to use a bigger washer. Here is my question..... On a lot of forums, they say "over torqueing a muzzle device will slightly crush a barrel and kill accuracy." If you think of it like a threaded fastener, yes you could theoretically torque it so much you distort the crown/muzzle by reaching the steels yield strength (where it will permanently be stretched.) But heat treated 4140 steel ha a yield strength of over 60k psi... So, because a over tightened fastener, that has not reached its yield point, will return to its normal shape, I should be okay right? I cant just take it out and shoot it, im still waiting for components to show up and the chassis to come back from cerakote.
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I know you 'should' use a torque wrench, but i dont have one and im already over budget for this build. The system that PA uses (if done with the right washer) should get you aligned within the torque spec. If you do the calculations for the effective area and clamping force, you would have to go to like 150ft/lbs to approach the yield strength of the barrel (im not strong enough to do that with a 10in wrench lol)
I installed a muzzle brake on a rifle one time and I torqued it pretty good took it to the range and it was shooting like total shit. Did a little research and came across a thread where a guy had the same problem. He took it to a gunsmith that told him that over tightening a MD will put pre stress exactly where you don't want it (near the crown) anyway the smith reinstalled his MD with the proper torque and his problem was solved he was back to shooting 1/2MOA.......Ok now to me I reinstalled mine and went just slightly more than hand tight and and mine went back to shooting great again.....so morale of the story is yes over tightening a MD will cause accuracy issues, but it can also be fixed by reinstalling with the correct torque.
Maybe you missed the part where I included my own personal experience with over torquing a muzzle brake and my rifle shot like shit then the only thing I did different was reinstall the muzzle brake with less torque and my groups went back to being great again.........should I just chalk that up as pure coincidence? If you are going to call out someone as full of shit and say they are wrong please explain why with a little detail or experience of your own.
Nah, you're wrong here GH41. It does (or can).
AMU dudes and a lot of other notable smith's figured out decades ago that the birdcage flashhider on an M16 can make an otherwise excellent barrel just about shoot the fucking jacket off a bullet.
That would be why they mostly just glue the things and use a crush washer to kinda halfass time it. We're talking about 3/8 MOA gas guns here, but the truth is universal.
Me? If it's a 100% precision minded rifle...it doesn't get threaded at all, because it's hard to over torque threads that aren't there.
To the OP: get a torque wrench. Borrow it from a mechanic buddy. Don't have a mechanic buddy? Damn...you need to work on that.
AMU dudes and a lot of other notable smith's figured out decades ago that the birdcage flashhider on an M16 can make an otherwise excellent barrel just about shoot the fucking jacket off a bullet.
That would be why they mostly just glue the things and use a crush washer to kinda halfass time it. We're talking about 3/8 MOA gas guns here, but the truth is universal.
Me? If it's a 100% precision minded rifle...it doesn't get threaded at all, because it's hard to over torque threads that aren't there.
To the OP: get a torque wrench. Borrow it from a mechanic buddy. Don't have a mechanic buddy? Damn...you need to work on that.
My question is: if you have the wrong shim size on it why not just remove it and use the proper shim instead of trying to over torque this one?
GH41 still waiting on a follow up from your bold response telling me I have been fed a big helping of bullshit. I thought for sure you would have came back with some factual data or first hand account to back up your claim. Please follow up soon as I am eagerly awaiting your educated response!
This may be the cause of the mystery problem on my stock remington barrel I had threaded by a local reputable gunshop. They said there wasn't enough diameter for 5/8 thread, so they went with 1/2". I put on a known good 1/2" threaded adapter but the barrel threads cut were interference fit, requiring a lot of torque with a big wrench. I swapped between my suppressor and a jp muzzle break, and the accuracy was over moa with the same batch of factory ammo it always shot 1 inch groups at 400 yards with. I'm going to pull the thread adapter off and shoot it and see what happens.
I want me some of that factory ammunition that shoots 1 inch groups at 400 yards. Surly you ment 1 MOA groups.
I got home and looked at the thread job. There is only .085 of barrel crown from the bottom of the thread cut to inside bore. I think that is a problem. LRI says you should have minimum of .10 and more if it is a magnum due to the higher muzzle pressure. Muzzle adapter wasn't as tight as I thought. I could thread it to the shoulder by hand. The crown is pretty rough. I might go back to the shop and see if they will cut off an inch of barrel and recrown it and see if it fixes it. I had tried a variety of factory ammo when I bought this rifle new and it shot amazing with hornady 180 sst so I bought a case of 200 same lot#.
