I have a 42" Montana BBL, 40 cal, prb barrel, deep rifling,1-48",  1" cut for a false muzzle on a Billinghurst underhammer target rifle.  It belonged to Bill Mowrey, he used a lot of them as I understand.  You can see the faint felt tip markings on the bottom flat.  They are highly regarded around here. 
I plan on putting Lyman Receiver and globe front sights and snipe squirrels at a golf course.
The false muzzle didn't come with it..."sigh"