So I am thinking of building a new upper for local Tac-Rifle Matches. I want a 18" barrel, but the (2) barrels I am looking at have different Gas systems. One has a mid-length, and the other has a rifle length. My first idea was a 16" rifle with a pig-tail to make it a rifle length system. Is there a "big" differnce between the 2 systems mid or rifle, or would I be better suited with one or the other.

I am still trying to decide if I want to put it on my current carbine lower with Magpul CTR stock and Endine buffer, or a new lower with a Vltor rifle length mod-stock and rifle length Endine? Would the 2 different systems cause problems on the 2 different lowers. As for comps I was thinking of a Cooley Comp, or TTI Recoil Ellimantor. Do you think that would pose any issues with the gas system?

Thanks.

The lowers/stocks should have no effect on the functionality of the uppers, as long as they're in spec.

Rifle length is a gentler system, since the gas travels further before expanding all the way up into the BCG, so it does more "Pushing" the action open, rather than "popping" it open.

The pig-tail will help that on a much shorter barrel, but on a 16", it's may not have enough power to cycle the action. You may have to enlarge the gas hole in the barrel to get it to work properly.

My advice would be to either buy a true mid-length system and stick with it, or buy a true CAR length system and stick with it. Both of them work, and are reliable, out of the gate. If you go changing things up, you're more likely to run into bumps in the road.

If you're like me though, you might enjoy the challenge, and the learning experience you'll get from it.

No question. For an 18" barrel rifle gas is the only way to go. It'll be 100% reliable and much softer shooting than the middy. Similarly, for a 16" barrel, mid gas is the only way to go. No need whatsoever for the pig-tail. PT's are a FUBAR bandaid solution for a problem that you won't have with a 16" middy.

As for comps, the TTI fared extremely well in a recent test, equal in recoil reduction to the SJC Titan and better in down force. I don't recall where the Cooley came in, somewhere after the TTI and SJC. The comp will not have any affect on cycling at all.