Looks good overall. Couple questions to make sure I understand a couple things.
Bayonet - why is there no cost? Do all rifles come with a bayonet included in the price? Or does "functionally a dagger" mean that you just buy a dagger and attach it to your rifle?
Gun butt and bayonet - do they get the enhancements of the rest of the gun or are they enhanced separately. Given the lack of cost, I'd assume that they either get the full weapon enhancement or maybe the enhancement bonus, but not the magical enhancements (e.g. you get +2 to attack and damage with the butt of a +2 flaming pistol, but not the d6 fire damage). I could see that making sense for gun butt, but Complete Scoundrel sort of set a precedent for bayonets with the bow blades (enhanced separate from the ranged weapon and an attack penalty), so I was wondering if you'd use those rules (probably dropping the attack penalty).
Random thought/suggestion (sort of depends on the answer to how gun butts are enhanced) - have you considered making rifles a double-weapon instead of a two-handed weapon? One end firing bullets or having the bayonet and the other end the gun butt. You would have the option to use only one and as a two-handed weapon instead (like how quarterstaff should be, but isn't). Just a thought, if only because it could be interesting to, say, have a character with knockback knock an opponent away with the gun butt before shooting him with the rifle end to avoid the AoO. Just a thought.
On the whole, like I said, looks good.