I run a lot of gonzo games. It's not uncommon for a PC in my campaigns to have a longsword in one hand and a machine pistol in the other. This brings the question to mind: How much damage does a longsword do compared to a machine pistol?
The most common answer to this question that I see is none. The level of tech shouldn't matter; just roll a d8 and move on. This answer doesn't really cut it for me. If a swordsman sees his foe whip out a Tommy gun, I want him to start sweating. But this opens a can of worms all on its own.
How much damage should a Tommy gun do? Should we account for sights? Automatic fire? Etc, etc. These questions are the first to come to mind but they lead down a slippery slope. In the long run, it doesn't matter if you perfectly simulate the finer points of firearms.
All that matters is that lasers deal more damage than guns than swords. And to simulate that I've implemented a rule I like to call 123 Past Present Future.
Basically, the weapon in question does 1 die of damage if it's from the past (relative to human history... or not!), 2 dice of damage if it's from the present, and 3 dice of damage if it's from the future.
For example, a longsword would deal a d8. Something like a chainsword would deal 2d8 since it requires levels of tech (machinery, fuel) that is more common in the current era. And a lightsaber would deal 3d8 damage.
The only trick here is finding what's equivalent to what. I would argue that a pistol is the equivalent of a modern day shortbow so it would deal 2d6 damage, but you might think otherwise...and that's OK!