(Assuming 1 ton of ammo. 1 heat sink, or 2 heat sinks in the case of an energy weapon.)
LRM20 has 3 damage per ton, per shot
AC/20 has 1.25 damage per ton, per shot.
Gauss Rifle has .88 damage per ton, per shot.
PPC has 1.11 damage per ton, per shot.
SRM 6 has 3 damage per ton per shot.
This is misleading because of the differing heat generation per shot of the weapons.
PPC generates 8 x the heat of the Gauss, and thus cannot fire as fast, for as long.
If we assume enough heat sinks to keep the various weapons cool (nearly heat neutral) and one ton of ammo, it begins to look like this:
LRM20 has 1.56 damage per ton, per shot. (needs 12 heat sinks)
AC/20 has 0.67 damage per ton, per shot. (needs 15 heat sinks)
Gauss Rifle has 0.83 damage per ton, per shot.(needs 2 heat sinks)
PPC has 0.30 damage per ton, per shot. (needs 26 heat sinks)
SRM 6 has 1.15 damage per ton per shot. (needs 10 heat sinks)
You can back off on the heat sink counts, to improve the damage to weight ratio at the expense of having to cool off now and then, but ton for ton, the SRM6 is pretty dang potent to start with, and gets better quicker than most other weapons as you back off on the heat sinks.
Also consider that you get 16 shots of SRM6 out of a ton of ammo (100 missiles per ton). Of the rest of the weapons mentioned (excluding the PPC) nothing comes within 30% of that Shot/Ton count (LRM20 at 9, Gauss at 10, AC/20 at 7), so the ammo is much denser in damage per ton terms. Which means you can carry relatively less ammo to do the same job, which means the damage per ton for the SRM6 gets better as you increase the ammo count.
Remember though, this is pure damage output. What you can actually put on target with SRMs and LRMs has quite a few variables. But for within 90m, the SRM6 is incredibly powerful for it's weight (and this is what makes the A1 Splatcat so fricking annoying... and popular).
Edited by Vapor Trail, 01 March 2013 - 11:22 AM.