Sling mastery affects steamguns.
Any check for "am I holding a sling?" will be happy if you're holding a steamgun.
Not tested for anything but holding one mainhand steamgun and using a skirmisher talent. SHOULD work with any talent, but I have no idea what dual-wielding will do. Either it'll error, or it'll be OP.

Adds the Raider sub-class, a versatile mid-range fighter who wields a sword in one hand and a steam gun in another. Disperse clouds of gunpowder and detonate them in brutal chain reactions, or lay low your foes with shotgun blasts.

Adds the Enforcer. Armed with shield and steamgun, the Enforcer utilizes suppressive fire and crafted grenades of all types to permanently remove foes.

Talent icons are from http://game-icons.net/ , cass icon is from https://opengameart.org/content/painterly-spell-icons-part-1 .

Increase the range of artifact steamguns to at least the range of an ordinary steamgun of the same tier.

Frequently Asked Questions:

Hey! I found an artifact steamgun with a short range!

Last Hope basic training in weapon shop.
Trains:
- Technique/Combat Training for 50 GP;
- Shoot (hidden talent) for 8 GP;
- Generic use of bows or slings (Bow & Sling Matery, generic talent tree) for 42 GP;
- Technique/Archery-Bow (class talent tree) for 200 GP;
- Technique/Archery-Sling (class talent tree) for 200 GP;
- Generic usage of steam-powered weapons (Technique/Steamtech) for 256GP;
- Normal (but still limited) usage of steamguns or steamsaws (Steamtech/Gunner-Training|Steamtech/Butchery) for 512GP;
- Steamtech/Bullets Mastery xor Steamtech/Battlefield Management for 1024GP;
- Access to tinker stuff in loot for 2GP.

p.s. I was very annoyed with inability of rogues for use of bows or slings.
p.p.s. ... and I like to craft things. Useful things.
p.p.p.s. fixed wrong branch upload :(