>>96796195
I've been looking at 3rd edition Vehicles to come up with weights for guns, gyrojets in particular.
4th edition UT uses the Launch Tube weight as the empty weight, with the only modification to the formula being that it multiplies it by the amount of shots.
>(R - T) x mWPS x S x M
>R is the mechanism factor, T is 0.5, mWPS is 0.1 for 15mm Gyrocs, S is the amount of shots, M is proportional to the amount of tubes
This has two big caveats: Barrel length doesn't matter, so for example an M72 and an FGR-17 (twice the length) would weigh the same, and given the Bulk values on the UT Gyrocs, they are very different in size.
The other caveat is that it scales directly with shot amount, despite these being empty weight, and there's no clear guideline for how many shots should be included in firearms with detachable magazines or belt-fed examples. A 30-round carbine would be as heavy as the LSW when empty, for example.
I'm not sure what factors to tack onto each length category (0.1, 0.2, 0.3, 0.5, 0.75, 1, 1.25 for guns), but as far as the ammo capacity goes, that could be somewhat mitigated by substracting magazine weight (WPS x shots x 0.5 or 0.2), but I doubt that would really fix the issue of having to choose an arbitrary amount of bullets.