Shim chart for timing muzzle brakes/suppressor adapters

[MCMXI]

I'm in the middle of installing and indexing AAC brake/suppressor mounts on three AI rifles and made myself a cheat sheet to help in picking the correct shims. While I was at it I figured I'd extend the table to cover some other "common" thread types. I discovered that M18x1.5 is the finest common thread out there which isn't helpful when trying to time a brake. I have shims with 0.001", 0.002" and 0.005" thicknesses and since a 0.001" shim rotates the brake almost 14°, the alignment can be off by as much as 7°. Anyway, maybe someone else will find this table helpful or at least educational. If I messed up the math please let me know.

 

[MCMXI]

I think this is an example of "in theory there's no difference between theory and practice. In practice there is". I found no correlation between the calculated rotation of a brake and the actual rotation for each shim thickness. I've resigned myself to using trial and error and assume that the discrepancy is due to the thread tolerances.

 

[Iron Sight]

??? is this to help sort out point of impact in regards to position of installed device?

 

[MCMXI]

No. The idea was that I could screw on a muzzle brake, use an angle finder to figure out how many degrees of rotation are required to properly time the brake, and then pick the best arrangement of shims to achieve the desired rotation based on shim thickness. When you think about how much rotation a 0.001" shim results in, and then realize the pitch has some tolerance, the chart isn't really that helpful.

 

[Theohazard]

Yeah, I've installed a bunch of different muzzle brakes and I've found timing charts to be mostly useless. I guess they can point you in the right direction, but they're never spot-on.

 

[Taurus 617 CCW]

I have installed 2000+ flash hiders and muzzle brakes on AR type guns. I only recently became aware that anyone had taken the time to come up with a system other than trial and error. Surefire has a colored shim set and a guide with their brakes. I thought it was interesting but it was never spot on so I just did it the way I always have. Your chart would work in theory if the machining was precise enough that all threads started at exactly the same point and stopped at exactly the same point. Due to the fact that there are 360 start points at one degree each, there is too much inconsistency. I will still use trial and error. I takes me just a couple of minutes to get the timing right using trial and error. Practice makes better.

 

[Arizona_Mike]

28 TPI is just under 0.036" per turn or about 0.0001" per degree.
Your results should be close to 10 degrees per thousandth.

For 1.5mm I get 16.4 degrees per thousandth. I can't see your chart on my cell phone.

Mike

 

[bikemutt]

I've found that Kentucky-torque, trial-and-error-back-it-off-one-more-time, and Rocksett is the answer.

 

[MCMXI]

Yep, that's what I'm back to now.