The RPG sources that I own list various effective and maximum ranges (or the equivalent in different systems) for shotguns, no two sets alike. The best I can gather is that they should somewhat outrange pistols, and can definitely hit 25 out of 25 moving targets effectively up to 47 yards away (an estimate of the longest distance in American trap shooting).

Shotgun rules ought to take barrel choke into account. This is a modification of the barrel, for most hunting and trap-shooting guns, that reduces the spread of shot (Mossberg had a diagram online a while ago).

Many RPGs neglect this, and quite rightly because most combat shotguns are adapted for close combat using cylinder choke (an unmodified tubular barrel). With this assumption, an effective range of not more than 30 metres, and maximum range for significant damage of 40-50m seems to be about right.

However, a shotgun with full choke is most effective, according to Mossberg who should know, at a range of 35 to 50m, by converting their diagram from yards. Their Choke and Load Usage guide supports this, assuming that human targets are most similar to Large Geese, which seems reasonable. You need heavier shot and more powerful cartridges to reach the longer ranges.

Modified choke falls somewhere between those. A shotgun pellet can travel up to 500m but it's pure chance that it would hit anything over most of that range.

My sources indicate that the range for major close-quarters damage before the shot spreads out is about 5 metres. That fits well with the published value of 6 metres. I propose to keep that.

I think, for RPG purposes, we can neglect modified and extra-full choke, and make rules for cylinder choke ("combat shotgun" range) and full choke ("hunting shotgun" range). In order that characters don't just use the second-named in place of the first, there has to be a clear advantage for the "combat shotgun" within its usual envelope. A -1 bonus at Medium range has the right mix of effects.

Thus, my proposal:

Combat shotgun (improved cylinder choke, includes skeet guns):

• Short range: 6m, -1 Accuracy, double damage
• Medium range: 30m, -1 accuracy
• Long range: 40m, +1 accuracy, half damage

Hunting or trap shotgun (full choke):

• Short range: 6m, -1 accuracy, double damage
• Medium range: 50m, +0 accuracy
• Long range: 70m, +1 accuracy, half damage

Nobody should try to shoot things at a weapon's long range, but it's physically possible if you can't wait for the target to get closer, not unlike shooting a pistol at 50m range.