I currently own a home defense/SHTF 14.5" AR-15. But I also have an Aero Precision AR-15 lower and most recently an Aero M5 stripped AR-10 lower that was on sale for around $100. Before the Aero M5, I had planned on building out the AR-15 lower to be a 6.5 Grendel to give me a precision long...