a buddy of mine asked for my advice about a 6.8 setup, but i have no idea how to answer his question as i have no experience with 6.8. what he wants is a RRA LAR 6.8 CAR-A4, but he wants to put a low pro gas block on with the Troy MRF-MF10 rail system. whats the barrel profile like? will any regular low pro gas block work along with the Troy rail system?

6.8's can be had in a variety of barrel profiles just like 5.56 so you would need to ask RRA if the gas block seat is the standard .750", which I believe it is.  If so then the only hang up would be the rail system.  I can't imagine that Troy made the rails in a way that wouldn't work with a low-pro gas block but I have no personal experience with that particular rail system.

One of the nice things about 6.8 is that nearly everything that works on a 5.56 rifle will work equally well on the 6.8.  While I can't give you definitive answers since I don't own either a RRA LAR 6.8 CAR-A4 or a Troy MRF-MF10 rail system I would be very surprised if there was a problem with what you describe.

Not to put down RRA, but there are other options out there that are better spec'd.

+1

If you're going to go to the headache of switching out out the gas block and rails, I would just buy a AR Performance or Bison Armory 6.8 barrel and build it.

Yeah, that's the ticket.

It's what I did.

Oh, +1

Me too!

But Ben at Bison is a great guy and puts out a really good product too.