It seems my previous post about tech levels and guns wasn't clear. People think I'm saying that guns do more damage the more technologically advanced they are, and suggest that guns actually become lighter weigbt and smaller in size over time.
Except: that second part is what I'm saying. So here's a restatement.
If I'm using (medieval-style) gunpowder weapons, the basic handgonne is a two-handed affair like a bazooka and does 1d6 damage. It otherwise works like a heavy crossbow, whatever rules I decide to use for those. There are also bigger weapons, which do 2d6, 3d6, and so on (I haven't set an upper limit, because I'm not striving for realism, just some variety.) These big weapons can't be carried by a human being, but they might be usable by giants. Otherwise, they're basically cannon.
With practice and discoveries, artillery and firearm manufacturers can make a weapon of a given size able to handle a bigger charge of gunpowder. This means that they can make a 1d6 weapon smaller, and the same applies to larger weapons. I picked an arbitrary period of one century; after one century, manufacturers can make a 2d6 arquebus that replaces the handgonne as the equivalent of a heavy crossbow, and there's now a 1d6 gun equivalent to a light crossbow (still requires two hands, but it's lighter and quicker to reload.) After two centuries, that gun size does 2d6, and there are 1d6 pistols available.
It looks like I'm adding a die of damage every 100 years, but I'm actually shrinking the size of the larger weapons. I figure it's the amount of gunpowder, basically, that determines the damage, and an explosion that could cause 3d6 damage requires a gun of a certain amount of weight to handle it without exploding.
Of course, this is a "six of one, half a dozen of the other" situation. But hopefully it's clearer what I'm saying now.