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Sig MPX install of Sig muzzle brake

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I purchased the LE version of Sig MPX PCC, it has a flash hider instead of the muzzle brake.  I ordered the muzzle brake from TTI, it came with the brake and

washer(not threaded).  I'm not sure if I should call it a lock washer, jam washer, or what?  The barrel itself behind the threading is tapered, no real shoulder anywhere.  I installed it with the tapered side toward the action, screwed the brake on, which stopped about a quarter turn short of 12 o'clock.  I tightened it to 12 o'clock.  After about 20 rds it was loose.  What am I missing?  No instructions were included with the brake.

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The washer you have is called a "crush washer" and you installed it correctly as the large end should face the muzzle device.   You use it just like you did, by tightening the muzzle device after it's hand tight to "clock" it properly, i.e. to have the vents oriented correctly.   


If there is no shoulder or other stop behind the threads the crush washer probably won't work properly and I recommend getting a "jam nut".   This is a thin nut threaded to match the barrel threading (1/2"-28 or 1/2"36 most likely) with wrench flats.   You thread it completely onto the barrel threads, then thread on the  muzzle device almost all the way and stop when it is clocked correctly. Then you back off the jam nut until it comes up firmly against the barrel device and lock the two together with wrenches.  That should keep the brake reliably tight but you can remove it for cleaning whenever you wish.  


Properly threaded jam nuts are available from most shooting supply shops including, of all places, Amazon.

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OK I will look, but it almost seems under that scenario I should eliminate the included "crush washer", which is unthreaded and has no flats to use a wrench.  It rests against the barrel at a point where it's tapered.  I don't do this often but I was under the impression a crush washer actually can be crushed, there is no shoulder to crush anything against.  The brake itself does tighten up against the washer, which is pressed against the tapered portion of the barrel.  I don't see any way the brake could be clocked properly if I put the amount of pressure on the brake it needs.

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12 hours ago, rider82 said:

PS, there is no large end on the washer, only a tapered side which I placed toward the action, and the other side(toward the comp) which is also VERY thin.

What you have is not a crush washer but a tapered “spacer”. When I replaced the flash hider on my MPX, I used alignment shims in addition to the tapered spacer to properly clock the compensator.



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