Re: LWRC REPR vs GAP-10
The biggest difference, of course, is that the REPR is a short stroke piston system and the GAP is a direct impingement gas system.
After that, the side-charging handle on the REPR makes manipulation easier (although different from your regular AR) and is suppressor-friendly in that it doesn't have a typical charging handle area that vents gas when suppressed.
The GAP has an excellent reputation for accuracy, but I confess to not having payed much attention to them.
The reports about the REPR are hit or miss, but mostly positive. Some owners see very good accuracy, but a few have reported groups that were not so great. I think part of that may stem from the fact that the REPR is a 1:10 twist (unless you specify a 1:11.25 in the 20 incher) and many folks may be running projectiles that are just too light for the 1:10 twist. At the lightest, they should get 168 grain ammo, and heavier is frequently better from what I've read. Still, there are a few reports that would indicate that groups string as the barrel heats, etc. Such reports are out there for any platform, so I don't know how much weight to put behind them. The majority of owners seem to be very pleased with the REPR, and it is LWRC's second best seller after their base A2 rifle in 5.56.
I love my LWRC A3, SL, and SPR in 5.56, and should be receiving my 16 inch spiral fluted REPR in the next few weeks.
If I were to find that the REPR were not accurate enough to suit me, then I would be ordering a Larue PredatOBR or regular OBR. Their adjustable gas block and forend are similar to the REPR, and reports indicate that a buyer can basically assume that any of them are going to be sub-moa - significantly so, often. And, they are made in Texas.