Short version: a good simple way to get realistic active point totals for firearms is to take the 5 root of the muzzle energy (in ft/lbs), multiply by 6 and add 5. In excel, that's =PRODUCT(ME^(1/5),6)+5 where ME is the muzzle energy. If you want a curve that yields more powerful guns, do the same but with 4 root, i.e. =PRODUCT(ME^(1/4),5)
Long version: Sorry for this wall of text
I am a giant military nerd. Traditional HERO gun damage tables, based on caliber, have always left me a little flat. After fiddling with Excel and Wikipedia data I think I have a good curve based on energy:
This curve follows the HERO chart range
(MUZZLE ENERGY(ft-lbs)^(1/5))*5= ACTIVE POINTS
But, if you'd like to see more variation in the common calibers:
(MUZZLE ENERGY(ft-lbs)^(1/4))*5= ACTIVE POINTS
Either way, the players can stat out any gun they fancy
Both of these curves have points where they fall apart. The 5 root fail point is higher in the cannon range, 35mm and beyond. 4 root falls apart right after .50 BMG, which is usually at the top of a heroic-level firearm chart anyway. 4 root guns do well in grim game worlds, along with making combat much shorter (the two often go together).
You'll notice this doesn't quite take into account things like overpenetration. Smarter people than I have taken a stab at that, and while it's a very clever implementation, it adds another layer to what is already considered a complex system. It's hard enough to sell my new group on HERO as it is. You also get into issues of what's important to you in game versus what's important to you in the real world. In the game, you'd probably prefer to take a few body than to be STUNNED. But in the real world, you would (I assume) vastly prefer to take a little break as opposed to losing a finger or a few cups of blood. Stopping penetration in the real world can easily lead to being knocked around a bit more, but any player is going to be annoyed if they pay points for a defense that gets them STUNNED more often.
One more thing: it's important for the GM to take the barrel length into consideration. If a player shows up with a 20 × 110mm Hispano pistol and claims the full muzzle energy, it would be cool for the GM to call foul on that. Along these lines, STR MIN calculations should also be checked and common sense used. Even if a character has a 30 STR, they do not weigh enough to anchor an autocannon firing light antiaircraft rounds. It will literally pound them into the earth.
Anyway, hope someone finds this interesting, and possibly useful. Next up for me: finding some Star Wars Hero prefabs. Older links in the forums appear to be broken. Unhappy face.
CartridgeEnergy.txt