Mil-Spec. or commercial?

All AR-15 receivers are made to the same dimensions, by reputable manufacturers. The milspec v commercial is usually in reference to the buffer tube and actual stock slid onto the buffer tube. Since that kit already comes with a buffer tube and stock, any

I used Del-ton's stripped lower receiver on mine, that I got locally, and it runs fine.

Mil Spec. according to Del-ton at: del-ton.com/ar_15_kits_s/1.htm