Personally, I think the guns you've designed in this mod are too advanced, they're practically modern firearms. You're only missing rifling and automatic fire.
I think a more apt level of technology would be muskets, which you guys refer to these weapons as being, but the descriptions provided sound like bolt-action rifles. Though I understand there are limitations to what you can mod, I'll still describe what I think would suit Dwarf Fortress better:
A more medieval design, the bullet would only be a lump of material, (Bone, wood, metal, doesn't matter.) that is muzzle-loaded into the rifle after the gunpowder. Each shot from a rifle is devastating when it hits, but inaccurate; and the rifle itself takes a long time to reload. Thus balancing the weapon against bows and crossbows, which have similar piercing capabilities but fire faster and more accurately.
One of the big advantages of gunpowder weapons in early medieval warfare was psychological. The loud bangs, smoke, and fire from the weapons tended to frighten soldiers unaccustomed to it, even though they were fairly ineffectual compared to bows and crossbows of the time. So a modifier on them that causes the weapon to frighten weak-hearted enemies might work.
Aside from that, I'd certainly recommend reading on some of the history of firearms, the wiki on muskets for instance: http://en.wikipedia.org/wiki/Musket
[ November 24, 2007: Message edited by: Slith ]