So are there rules somewhere for generic this caliber bullet does X damage, and has these other stats or anything? I've always been curious to figure that out.
My cousin and I are working on a random firearm generator for Borderlands style loot, and we've basically just had to freeform everything, but if there is a general convention at play we could totally make it legit.
The idea right now is that the weapons are broken down via proficiency slot, and then you roll on a table. So for instance, you roll on the Pistol table and you can receive either a handgun or revolver. Then it rolls caliber of ammo, number of shots in the magazine, extra tweaks to the firing mechanisms (like upgrades and stuff), then appearance and accessories. And at the end it gives you your weapon's stats and if there are any special features like fire damage, or extra gadgets and the like.
Oh, and since he's a programer, he's making a flash program that will do it at the press of a button along with the option to reroll each individual option as needed.