It’s always a balance in games between granularity and ease of use. When it comes to weapons you need to balance the desire for different weapons to have advantages and disadvantages with the desire not to have everything become too burdensome.
I want to emphasis the skill of the character over the worth of the weapon, so bonuses will primarily come from character skill and development. A lot will come down to roleplaying, the description of the weapon and how it works.
A silent weapon, for example, may have no game mechanic effect but when used it’s not going to make any noise and so isn’t going to alert any guards (provided you manage to take someone out in one shot).
Standard weaponry is unlikely to stray beyond the -1 to +1 range of bonuses.
A friend of mine, Tim, has long argued that damage ranges on weapons should include a ‘1’, allowing for a full range from glancing blow to deadly hit and that’s been weighing on my mind while I’ve been restructuring my notes for MotSP and I think there’s merit to it. Weapons are, then, likely to have damage ranges from 1d4 to 1d12.
There are exceptions to the above of course. Exotech (pronounced Ex-Oh-Tek) are the relics and leftovers of past, advanced civilisations. They’re the ‘magic items’ of this universe and so they can break all the normal conventions.
Ammo I’m not so sure about. It can be a pain in the arse to keep track of so either ignoring it or abstracting it are options. How do you feel about keeping track of ammunition? Do you like to track it down to the last bullet or would something like an ‘ammo save’ after each combat suit you better? An automatic weapon would have a low ammo save, while more precise, single shot weapons would have higher ammo saves (roll under not to spend a ‘mag’).
I’ll include how weapon saves would work in the weapon lines below:
Example Weapon Line:
Burning Hand-Beamer, Accuracy +1, Damage 1d8 (heat), Range: Short, Ammo Save: 10
Burning Hand-Pulser, Accuracy +0, Damage 1d6 (heat), Range: Short, Ammo Save: 15