Does the Gun Mage spend spell slots to use them as auto reloading bullets? If so then that would be OK in my book as long as they are not 0 level spells. Blow a spell slot in a pinch to auto reload on the run for example.
Sniper looks like it has potential. I would suggest the crit multiplier to instead have all damage maximized on the dice per a critical or follow the way the Assassin PrC handled the ability.
Looks like a decent book that needs to go back in the oven for a bit more cooking.
No, they don't cost grit or spell-slots and can be conjured as a free action. They last 10 Minutes, i.e., a gun mage could supply multiple allies with bullets. Only if you want to reload as a free action, you have to spend 1 grit + a spellslot of 2nd level or higher to reload as a free action with the conjured bullet - you essentially create it in the gun, all loaded.
This pdf had potential galore and utterly wasted it.
Seems to be a mistake in your review or in the PDFs terminology, as "adding 1 to the crit range" would normally mean the number you have to roll to threaten a crit. So the sniper doesnt steadily do more damage if he gets a crit, but rather has more of a chance of getting a crit if he takes time to aim, which makes sense. In that regard a +1 to crit range is actually pretty weak on a weapon that is normally a 20/x4, since 4 rounds of aiming gets you nothing but a 15-20/x4 which while impressive, is only a 25% chance to do the damage you probably would have done otherwise if you shot each round. Unless of course the crit range increase is applied before Keen, in which case it becomes pretty good (and still not broken)
I also pretty strongly disagree on your assertion that free ammo is a huge problem that will unbalance guns, but thats a matter of opinion.