Only problem w/Aero M5 was recoil system that was corrected by changing buffer tube extention,spring,and buffer to Armalite AR10 parts.For carbine setup.My BCG is Nickel boron that had to be worked in due to coating,was very tight out of the box.Got better the more I shot it.Aero has alot of value for the money.Just my 2 mags.