Yep any AR lower will work with the 5.7 upper. Since this was for my daughter I went all out and started with a Spike's tactical lower, slapped in a Timney trigger (set to 2.75 lbs) and dressed her out with MagPul furniture. Very pleased with the end result. snappy little round the 5.7, shoots fast and flat with an effective range of about two hundred yards then she starts dropping off. It's an up close and personal thing. Recoil is not much more than a .22 & the fifty round mags are a plus