I am thinking of building a SPRish (sorta) 18'' flattop. I am looking for a A1 or A2 upper for my carbine (decided I don't want optics). Plan on building a iron-sightless scoped hunting/varmit gun out of the flat-top receiver I'll have spare.

Plan on using my A3 RRA upper, and my A2 stock. But anyways. What gas system does the RRA 18'' varmiter barrel use? Anyone sell a good SS HBAR in 1/7 twist? I'd love to have something like that so I can shoot 77 grain bullets for deer hunting.

BTW if you know of anyone selling a A1 or A2 upper let me know.

I think the RRA 18" barrel uses a midlength gas system.  That's what it looks like from the pictures anyway.

It is definetly long than the standard carbine system. I wanted to make sure before I purchase anything. 18'' seems like a good choice for what I am doing. So I should try to build around that.

My 18" from WOA has a full length gas tube.

I guess I'll have to call ADCO and find out for sure before I order one. I'd rather it be a full length. So I will have more options for free float rails. I may just go with the RRA quad free float rail.

I just (earlier today) ordered a custom Kreiger 18" SS 1/7 MIDLENGTH match grade barrel from John @ WOP.  In 8 to 10 weeks I'll let you know how it shoots.