heres something to think about. if the katana could cut through metal in the way people seem to be saying on message boards across the web then why did the japanese wear armour? if their swords cut through steel and iron why woud anyone wear a full suit of armour that limits their movement(which it must do putting on a suit of armour adds weight if nothing else). furthermore I dont doubt that weapons could readily cut through helmets, just look at history, the well crafted and tried and proven Roman helmets were defeated by weapons crafted by people with skill in metal but nothing approaching the Romans, the Dacian Falx(and according to some records the remnants of the Thracians who still used the Rhomphia) were able to cut through the helmet and kill the soldier, the romans hads to add in reiforcing bars to try and stop them and even these had only limited affect. remember thes epeople were moving and fighting and still had their helmets cut through by inferior metal technology. heres a point about how effective armour could be and this how difficult it would be to cut through a rifle, check European fighting methods, as soon as fully articulated gothic plate armour(which I have seen worn and used by the ARMA) came about fighitng methods changed, swords narrowed and became highly tapered at the ends, half swording became common place and targets for the blade shifted to attack joints and gaps, if metal could be cut through by high quality weaponry such as this the why were techniques like this devised? for kicks? No because it was almost immpossible to defeat Full Plate without these techniques. what does this prove? well not much as I have no hard evidence on me just what I have read and thought of myself after looking at things, but if fighitng techniques had to adapt to armour then surely the armour must have caused problems for swords, so why would a metal rifle barrel be cut through if a sheet of that is thinner cant be?