Machine-guns are fun to shoot but unless you have a metric fuck-ton of money to dole out on ammo, what's the point? They're novelties. Problem is the ATF determination that bump stocks are legal is based on mechanical function of the firearm itself. So if I go and put a full auto fire control group on an AR, I've illegally converted it. If I put a bump stock on it, I'm not changing the guts of the rifle at all.