The problem I have with Weapons Locker (and I think Ultramodern Firearms is the same way), is that it's based on D20 modern, so what you get is a whole book full of guns that are nearly indistiguishable stats wise. Hmm...do i want the H&K MP5 at 2d6 2x20 or do I want a Desert Eagle .50 at 2d6 2x20..... While this might be realistic, it's also boring, and basically leads to an any old gun will do philosophy, why do I care if they are all the same anyway. That's one of the things I like spycrafts weapons rules, it may be less well balanced, or a little more confusing, but it's alot more fun to play with. You ask a spycraft player what his weapon of choice is you usally get back a specific answer ("AR-15", "MP5KS", "Glock 30"), you know what my d20 modern character has....a handgun and a shotgun. Anyway, ranting aside, I'd avoid all three and go buy a real world weapons book like Jane's Gun Recognition Guide, that has good picture (because the way a gun looks is about as important as how it stats in an RPG), and a decent selection of civilian and military weapons to choose from. Most of the system have fairly simple conversion rules, and you get a system agnostic solution.