Yes, Northern Crown has rules for firearms and artillery from about 1600-1700. They include accurate reload times, rules for misfire, gun-related feats like Take Aim, Both Barrels, and Hair Trigger, and cinematic gun tricks like shooting the ram rod, double-shotting, and improvised small shot. Not to mention baroque sci-fi weapons and technologies like multi-barrelled quick-loading volley guns, heliopyritic mirrors and electrostatic gunlocks.
A caveat emptor from the author: the gun rules in NC at first glance seem to offer little or no advantage over bows and arrows. From a purely min-maxing perspective, this is true, but not the whole story. What matters is the relative effectiveness of the first volley: two-handed guns do more damage and have much better crits than bows or crossbows, and so are particularly well-suited for the ambushes, duels, frontier sieges, and pike-and-shot volley tactics of the NC universe. Twenty muskets doing d12 (or 2d12 if double-shotted, albeit with a 5% chance of bursting the barrel) with crit ranges of 17-20/x2 vs. the same number of bows doing d8 with crit ranges of 20/x3: which side would you rather be on after the first volley?