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crush washer


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OK guys, I have now my first problem with my build. I am down to the final assy and the damn crush washer is giving my trouble. I will try to load a picture later , but for now here is my problem. The break I have allows the flash and excess whatever to go out the sides and on the upper ( or lower side) there are 2 small holes I want them at the top s if ever in the prone dust is not blowing up and the muzzle is staying down. The washers I got from brownells and it was the thinner of the 2 I saw.

How much pressure does it take to crush the washer? All I need is a 1/4 of a turn to get the break where I wnt it.

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If I recall correctly, the 5/8"-24 thd on most 300 BLK barrels, works out to around .015" linear movement for 360 degrees rotation (one revolution) so 1/4 turn would be about .0035" linear movement. Personally, I don't really like crush washers preferring the shims or facing off material from the MB, but if you feel that your already torquing the MB as tight as you want to go, you can always, get a piece of emery paper, and using a flat surface, just make figure 8's with the crush washer (or the back of the MB) until you remove .002" or so.

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Thanks for the info I will remember it for sure!

I got it, I went out to my shop and looked around and I came across an old wooden vise so I took a paddle bit and cut me a 5/8 hole glued in some plumbing rubber gasket material and clamped the barrel down then moved it to the vise. I then took and tightened and loosened several times and had little luck then all of a sudden I very very slowly tightened the break untill I had it right. I did sctratch the break up a little from the wrench being taken on and off.

I will load pictures in a few.

Also I should have my ammo by the 15th so I hope the Range is ready for me.

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If I recall correctly, the 5/8"-24 thd on most 300 BLK barrels, works out to around .015" linear movement for 360 degrees rotation (one revolution) so 1/4 turn would be about .0035" linear movement.

Let me start with a disclaimer: I'm not trying to start an argument or be a smarty-pants, I'm simply opening myself up to the possibility that my way of thinking isn't correct, and I want to know the math behind your conclusion.

Having said that:

I'm getting different math here, to me 24 tpi means that one full revolution is 1/24th inch linear travel, and for me, 1/24th = .0416" decimal. Using my (possibly flawed) math, 1/4 turn comes to .0104" linear travel. Am I way off base or what? This is really important because I'm getting ready to have a muzzle brake timed and I'd like to know the correct way to calculate how much to mill off the back to yield X degrees of rotation.

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You are, of course correct. I need to go to the trouble to verify things that I post instead of just going by memory. It's good that you called me on this because when I am timing one of these things or a barrel nut for a rail, I always go to the trouble to double check the math. As you might be able to tell from the opening of my reply, I was going by my recollection and didn't bother to double check before posting. I'm glad that it apparently didn't cause 6132 expert to take off too much material, in fact since my math was off in the other direction, he would have been taking too little off even if he had followed my advice, But in the future I intend to try harder to proof my posts/replies so as to not cause someone to screw something up because they followed my advice.

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the term timing the comp, refers to lining it up in such a way that the holes/ports are oriented so that they will be most effective in counteracting the forces placed on the gun by the projectile while it travels down the barrel, that and the recoil from the charge, since the line of the bore is above where you hold your gun, it wants to rise, that is why they put holes on the top on some MB's to counteract that. also the bullet traveling down the rifling in the barrel wants to twist the gun in the opposite  direction, so you will see on some that there will be holes that are located asymmetrically to (hopefully) counteract that. Based on the fact that there are so many designs out there that are so totally different from each other, I think that to a great extent compensator/muzzlebrake design seems to be as much art as science. kind of like surf board design.

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Jgun was precisely right in the way he explained it. Timing just refers to the way a threaded object is oriented at the end of it's travel. To show you an example, let's use my muzzle brake.

Lets say I want to mount my brake WITHOUT using a crush washer, this means my muzzle brake will thread all the way back to the shoulder at the back of the threads on the muzzle. If I get my brake threaded on and tightened to the 65 ft lbs recommended and notice that the holes intended to be on TOP of the brake are on the bottom or to one side, my brake will have to be timed.

So lets say for the sake of example that I notice that the holes are 90 degrees counter-clockwise from where they are supposed to be. I will need to know exactly how much material to remove from the back of the brake in order to get 90 more degrees of rotation. In my case, I know my brake is thread at 24 threads per inch, which makes the math very easy. Every full 360 degree rotation moves my brake towards the chamber end by .0416 (or 1/24th) inches.

We need: 90(degrees we need to rotate) / 360(full rotation) = .25 (number of rotations needed)

We'll get: 0.25 x 0.0416" =  .0104"

So by the math we can see that for 90 degrees of rotation, we can remove .0104 inches from the back of our brake to time it correctly.


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When I mentioned timing the barrel nut, I was referring to one of the railed hand guards that I installed, that when I tightened the barrel nut that came with the rail and then installed the rail and bolted it to the nut, there was an unsightly gap between the back of the rail and the top rail of the upper receiver. The only way to correct the problem was to remove some material from the barrel nut in order to move it, and the rail, further back, but it was important that when the nut was tightened on the receiver the mounting holes for the rail would be oriented properly. This is not something you will be likely to have to do. In fact most handguards are designed so this is not required, BUT, once you start mixing and matching parts, especially with the .308 guns, things start to get more interesting. If you have been building these things for a while I'm sure you've already encountered the part that according to the mfg should fit, but in reality doesn't. That is where you will have to use your imagination to figure out how to make it work.

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