I see that PSA is offering a "Marauder" AR upper with nitrided barrel, 5.56 chamber, and a 1/7 twist rate. It looks pretty cool with that can-like flash hider, but I think I read somewhere that 10.5" barrels were the shortest that could cycle reliably. Am I wrong in this regard? Can a 7" barrel work without excessive FTF's or FTE's? Any bullet weights to avoid with such a short barrel?