Large sized Rail Gun dice

[ptlans]

I'm running a game for my pathfinder group and I'm hoping for them to stumble upon a large sized rail gun with only a few rounds of ammunition. They might be able to use this against a very powerful enemy later.

The problem is I'm uncertain what the damage dice for a large sized rail gun would be.

Medium sized is 3d10

[The Mad Comrade]

6d8