So I just got a Colt 6940, and I'm very pleased with it so far. Got 200 rounds through it without a single problem! The first thing I want to do is upgrade the trigger. I was thinking about an RRA two stage National Match. I was checking RRA's site at Rock River Arms: NM Two Stage Trigger And I noticed that there is a "sporter" version to fit "large pin lowers". My rifle is marked "Sporter M4 Carbine". What exactly does this mean? Do I have to get the sporter version of the RRA trigger and in general what do I need to know about any other parts and their fits?