Cutting the barrel down past 18" is silly IMO.
One, you lose the ability to take off the comp/brake and with some matches allowing IRON-SIGHT and NON-Ported/Comp'd Saigas in Tactical instead of open, being able to take off the brake is something i would want.
Also, you'll get MUCH more performance out of CHOKES than you will with any other muzzle attachment. For the muzzle brake to do anything, it needs to vent gasses away and most 12ga attachments have very little surface area to work with.
IMO, if i were starting over and making a 12ga competition gun i'd do the following:
Gh