Sometimes the BAR comes with the BOSS already screwed on the end of the muzzle.

It works, but it is complicated, but if you figure it out, it can help, my dad has one on his A-Bolt 7mm Rem Mag, it does make a difference, but I find that my Remington 673 in .308 Win.actually shoots consistantlybetter.
It'll probably get better once I get ahold of some Outer's Bore Foam.

Josiah