Modern and Sci-Fi settings always present a bit of a challenge. Obviously the weapons are more effective than those from the 1920's, but at the same time, if you make them too powerful, you effectively undermine the whole point of Lovecraftian horror. If any old grunt can carry a weapon that can take out a Formless Thing in a single hit, what was previously an unspeakable horror ends up as simple cannon fodder!
To avoid this sort of thing, my inclination has always been to scale the weapons for each setting. For example, use tommy gun stats for a pulse rifle. So long as you don't try to mix weapon lists from different periods, this works fine. The alternative is to actually create a 16" range / D3 rate / D+4 damage / AP3, strafe weapon, potentially with something like a -1 DEX bonus for laser sighting, but this is going to be at least an 8BP weapon.