Hi I was wondering if I could drop my m4 bushmaster upper on a 9mm lower, or do I have to have both a 9mm upper and lower? - and also just out of curiosity will a pistol sized AR upper (11.5", etc) drop on a regular lower or do you need a pistol lower as well- (legally of course w/class 2 sticker) the same goes for a 9mm short barrel (pistol sized ar upper)- would it work with a regular lower or not??? Thanks for any help on this matter!- oh and could anyone give me your best sites for buying uppers/lowers of different types/calibers and sites for cheaper accesories/flip up and reflex sights/ custom stuff, and all AR-related goodies, etc... And one other question- I just bought a Bushmaster M4 with a quad-rail freefloat handguard and I was told that it couldn't be removed from the gun... Is this true or not, because I really want to get one of the new RRA half quad/half alluminum freefloaters- so any help would be much appreciated! PEACE*&*GUNS a.Truetone PS- any good sites for buying ammo-both bargain/specialized type for any calliber???