Yep, I am building a .45 SBR. The biggest challenge with using a standard lower is mags. The 16 round Uzi mags are big bucks now and hard to find. I only have 2 of the converted Olympic ones. Olympic keeps talking about making new ones but won't give a date. People have modified grease gun and sten mags to work. If you're considering .45 I would read through the .45 thread on the other AR site so you know what's out there and what has been done. Feel free to PM me if you have questions.