I am building another 6.5 Grendel upper and I want to use my MRS-2 on it. It's an 18" SPR-ish barrel, and I want to use the new 15" Seekins SP3R forend on it. My question is, will I have room for the MSR's collar if I use the 15" rail on an 18" barrel? If not, I'll have to use the 12" rail instead.
I guess I should clarify... By my calculations, from the tip of the muzzle to the back of the MRS collar should be about 2.75" or so (.620" threaded section + .700" stepped section + 1.4" for the collar). If the barrel is 18" and the rail is really 15", that doesn't leave me a lot of room to play with. I know I'd be safe with the 12" rail, but I'd really like to go 15" if I can.
According to this picture, I think I'll be alright. I'm just looking for a bit of reassurance before I drop the coin on a 15" rail:
Depends on where Seekins is measuring the rail from. Ask what the gross overall length of the upper is to determine your measurements. I would guess that you will have about a 1/2" gap from the end of the rail to the back of the suppressor. The back of the collar should just about line up with the front of the rail.