Okay the achievement is unlock every weapon which is
7 standard weapons-assualt rifles and energy rifles
7 short range weapons- shotguns,revolvers,flamethrower and a akrid launcher
7 long range weapons- snipers and plasma snipers
7 heavy weapons- rocket launchers,hand cannons and thermal launchers
7 Support devices- shields,injection gun and v device
then theirs the grenades 5 in each categorey
5 standard grenades
5 dummy grenades
5 plasma grenades
5 disc grenades
5 release grenades
all you do is keep spinning the slot machine and then eventually you will unlock them all i actually unlocked all the abilities and character parts before the weapons so it will take you a while especially when each spin of the slot machine goes up to 10,000 credits per spin