So I finally got around the removing the factory Sig flash hider / suppressor mount on my Rattler LT and installing a Surefire SOCOM 7.62 3-prong.

Best method is to remove the barrel and put it in a padded vise using the gas block for anti rotation. The FH came off pretty easily using a socket size that matches the tines. Heard they can be on there really tight so not bad so far.

Got a new Sig donut adapter from Sig, pre-tightened it onto the barrel until it didn't compress anymore, got the shims stacked up, Rockset, overtimed it, took apart, clean up Rockset, adjusted the shim stack, Rockset, timed it, put the gun back together, inserted suppressor alignment rod and...

Not centered, pretty far off. Damn it.

Pulled it all apart and cleaned up the Rockset. Tried to get the donut off with a wood punch and hammer, no luck. Tried vise grips with rubber gasketing to protect the donut. Gasket ripped and scarred up the donut. Damn. More banging on it with a nylon hammer, got it off.

Tried again with hand tightening and indexing the donut 180 degrees. Seemed to be better. Pre-tighten to seat donut, remove the FH and the donut pops off. Won't stay on now. A little Rockset to hold the donut, pre-tighten, remove, shims, Rockset, torque...

Still not centered. Shit.

Take it all apart again. Wail on the donut with various wood and plastic punches to get it off. Clean up the Rockset.

Grab the old donut from my original Rattler that was a little scarred up after removing it. Between two different 7.62 3-prongs, two chamfer adapters, mixing and matching them and indexing the donut to various timings, got the alignment rod sorta centered with everything hand tight.

Torqued it all up and timed with ONLY the chamfer adapter and no shims. A small miracle.

Rod is reasonably centered, a little flex in each direction to contact the suppressor, not perfect but seems good enough to avoid a baffle strike.

I'm not really sure if it's the barrel or the donut. Both donuts had similar effects but the one that wouldn't stay on after being removed the first time is probably a bit worse. If both the barrel and donut are a little bit off, the different timings of the donut would cause the alignment to change so that's probably what's happening.

Sig really needs to just have square shoulders on their barrels or make it an option. Their own FH/Mounts would be fine on a square shoulder and the taper that is really for a direct thread can is no longer needed because why go direct thread with all the QD mounts available?

For the record, I've put Surefire FH's on two Colt 6960's, 4 Criterion AR barrels, two Aero AR barrels, an HK MR556, and an HK MR762, and all of them were centered well enough not to re-do. Even my original Rattler 5.5 wasn't this big of a pain.

This message has been edited. Last edited by: Lefty Sig,

I had a similar experience with the MPX, which is even worse with 13.5X1 left-hand thread AND a tapered shoulder. Well guess what? The European standard 13.5X1LH is designed to index off the muzzle face. It's no wonder the MPX is notorious for poor accuracy.

I actually lucked out with my MCX since I have DeadAir suppressors and they make KeyMicro muzzle devices with the SIG taper. I got perfect concentricity with those and my DeadAir Sandman (men?).