Can anyone provide the proper way of timing a muzzle device using the crush washer?

I have a FSC556 that I installed on my SCAR 16S to replace the FN-equipped model (the FN version was missing the rim, so the washer/shim would actually squish out) but I wasn't sure how tight to get it. So I turned it about 45 degrees after hand tight using a wrench to get the logo at the 12 o clock position. After 300 rounds, it spun off by itself.

I heard I need at least 90 degrees but not more than 460 degrees?

With the crush washer, if you achieve 15-20 ft-lb torque at less than one revolution from hand tight, then you leave it there. Sounds like you didn't achieve that torque, so you needed to go around once more. This does require you to have a torque wrench to make sure you're getting the required torque spec (i.e. the washer has indeed started crushing properly) at that short of a rotation from hand tight.

The no-torque-wrench method is to always go at least one full rotation past hand tight.

The torque spec doesn't appear to make sense for a crush washer, and because you need to time the muzzle device. I know what the TM states, but it never made sense to me for the A2 w/ the crush washer.

I used a new crush washer, but I think I didn't tighten it enough. Will I really need one full rotation after hand tightening it? I was going to do about 180 degrees or 90 degrees after hand tightening. I don't want to overtighten it.

From what I have gathered, the tq spec only applies when you are using shims, not a crush washer.

And also from what I have seen, you should get at least a 90 degree turn from hand tight, when using the crush washer. If your muzzle device doesn't need to be timed, I would go maybe 120 to 180 degrees and call it good. The minimum 90 degrees means you should have a min of 90 if the device needs to be timed. If it doesn't need to be timed, such as an A1 flash suppressor wouldn't, I would never barely go to 90 degrees. I would always surpass it by a bit, but not necessarily 360.

I just checked again last night, and I either go without shims and turn the FSC556 about 300 degrees to time it, or I use about 5 shims to turn it about 200 degrees.

For some reason, it wasn't this difficult to install on my 16" M4 barrel - I just stuck it on there and turned. It stayed on at the range with the same number of rounds.

How much of an impact will I have on the muzzle if I crank down on the crush washer? I thought AMU said something like no more than 5 ft-lb of torque and to use red threadlocker?