Assembling two AR pistol lowers. One of the lowers is the Foxtrot Mike Products .45 ACP FM-45 lower receiver, and the other is a "standard" AR-15 lower receiver I picked up from Palmetto State Armory.
I'm an idiot; so, here's a quick video on how to replace the magazine catch on a Foxtrot Mike Products .45 ACP lower. FYI, Foxtrot Mike has awesome customer service!