I am newbie to building an AR-15. I have purchased a Stag and a High Standard lower reciever, two Stag lower parts kits and now don't know where to start with the uppers. I have seen M4, A4, A2 and so forth but don't really know the difference between these. I would like to put on a complete upper from Stag (H2) but don't know what type it is. Need some knowledge from you all season builders on this forum. I would like to build a good CQB and a good match riffle.

Joe

Here's the quick rundown:

M4 = Flat top upper with 14.5" or 16" barrel with turned down section for M203 grenade launcher mounting.

A2 = Carry handle upper with 20" barrel.

A4 = Flat top upper with 20" barrel.

Thanks for clearing that up. So I guess that CQB will be a complete Stag upper and the match riffle will be a CMT upper with a bull stainless 20".  I am correct with these build?

Joe