UC is Ultimate Combat, a Paizo product. It is slowly being added to d20pfsrd.com right now, some is up, a lot still isn't.
I have no idea about the gunslinger class, I haven't been able to bring myself ot fully read it and the gun rules. Every time I try, I have to stop lest I give in to the urge to repeatedly face-desk. All I can tell is that the gun rules are ridiculously broken, they're just plain better than other weapons, get to hit touch AC at 1st range increment (or even the 2nd or 3rd with the right archetype or item!) and get to break the rules by benefiting from Deadly Aim even though it's a touch attack and being able to be used with sneak attack (why can't I sneak attack with EXPLOSIVES again, Paizo?), and other bull that spits in the face of game balance.
To make matters worse, to "balance" them, guns and ammo are expensive. But gunslingers and most gun archetypes give you one for free at level and the ability to FREELY make ammo (apparently the standard 1/3 cost for crafting wasn't good enough, or maybe they just felt like kicking more rules in the nuts). The "drawback" is your gun is slightly broken and only you can use it properly, so it can't just be sold. Oh noes, an uber weapon at level one that my enemies can never ever use against me! That's such a massive drawback! /sarcasm Amazingly worse still, the degree to which guns will completely rape your game depends on the "tech level" the DM decides to use. If he chooses primitive and low availability, guns will be overpowered but rare and...that's supposed to make it ok, I guess? If he chooses high tech and common, you're an idiot to not use a gun, all other weapons are completely pointless and obsolete. Instead of just mechanically balancing guns with the other weapons, the designers decided to leave it all up to DM Fiat / "Mother May I?"
That's as far as I've delved into gun rules so far, but it's enough for me to know I will simply refuse to play in any game that uses them.
EDIT: Oh, also, the misfire rules. Are dumb. Balancing overpowered weapons by a random chance of them breaking is terrible game design. And the scatter shot is the most overpowered thing I've ever seen. It makes Whirlwind Attack look like complete horse
and is available without a feat on guns, presumably from level 1. Weapon damage in a cone FTW! The most insane part of it is, the way scatter's written, it's actually BETTER for avoiding misfiring than normal shooting. Because...well...just read it!
[sblock]Scatter Weapon Quality: A weapon with the scatter weapon quality can shoot two different types of ammunition. It can fire normal bullets that target one creature,
or it can make a scattering shot, attacking all creatures within a cone. Cannons with the scatter weapon quality only fire grapeshot, unless their descriptions state otherwise. When a scatter weapon attacks all creatures within a cone, it makes a separate attack roll against each creature within the cone. Each attack roll takes a –2 penalty, and its attack damage cannot be modified by precision damage or damage-increasing feats such as Vital Strike.
Effects that grant concealment, such as fog or smoke, or the blur, invisibility, or mirror image spells, do not foil a scatter attack. If any of the attack rolls threaten a critical, confirm the critical for that attack roll alone.
A firearm that makes a scatter shot misfires only if all of the attack rolls made misfire. If a scatter weapon explodes on a misfire, it deals triple its damage to all creatures within the misfire radius.[/sblock]
So, by sheer odds you'll basically never ever misfire. But that's ok, because if you do, the random effect will be slightly more severe in magnitude! Yay game balance! Side note: Pretty sweet getting to make attack rolls yet telling miss chances to go screw themselves if you're into broken rules, eh?
