The Soldier class should have Profession (military) as a class skill -- oops!
As for the gun rules, here was my design philosophy for NC:
--Guns should be slow and cumbersome to use -- this is a game of derring-do and heroic action, not gun-fu. On paper, they're not much better than longbows. Guns are good ambush weapons, siege weapons, and holdout weapons, but are not meant to be the focus of combat in NC. In most NC battles, the PCs fire one volley then draw swords and have at it, maybe saving a loaded pistol for a coup de grace or stray shot.
--Guns should have a good chance of putting a 1st-or 2nd-level mook into negative hit points, but a PC of 3rd level or higher should have enough hit points to survive the odd shot. I think of hit points as "ablative plot armor" rather than health -- the more important you are to the plot, the more attacks against you end up as grazes or near misses. A defense bonus seems redundant under that definition of hp. In my d20 Modern games, it seems that high-level characters can stand toe-to-toe and unleash clips of ammo at each other and still miss. That wasn't the feel I wanted for NC.
--NC is a low-AC world, but the NC core classes were given class abilities to make up for it -- the "just a scratch" ability of rakes, the insight AC bonus of agents, the magical defenses available to witches and their black garb AC bonus, the improved cover and concealment of the scout, and the scientific phenomena and inventions of natural philosophers. There's the shield bonus to AC for PCs with the Fencing feat, too. I think this makes up somewhat for the lack of D&D-style heavy armor.