This was a topic in another thread and I worked out a possible addition/change to the Gunsmith class feature. Everything from the original would be kept, but the additional stuff in the spoiler below couldbe added. It think it would allow the gunslinger a wider option for their chosen firearm, and give then incentive to keep their 1st level firearm, and allow them to enhance their chosen firearm much like a wizard can to their Bonded Item. This was posted elsewhere but it seems noone if checking it out. So, I'm reposting in its own thread.
Starting at 1st level, as a standard action, the gunslinger can perform a quick clear action to remove the broken condition from this firearm, as long as that condition was gained by a firearm misfire. At 5th level, the gunslinger can perform this maneuver as a move-equivalent action, and at 9th level as a swift action. Additionally, at 7th level, as a standard action, whenever the gunslinger rolls a misfire with her bonded firearm that has the broken condition, she can keep the firearm from exploding, though it retains the broken condition.
Upon reaching 5th level, once per day, the gunslinger can use her bonded firearm to perform any one deed that she has access to without having to spend or maintain required grit points. This deed is treated like any deed other performed by the gunslinger.
In addition, a gunslinger can add any of the following weapon properties to her chosen firearm as if she has the Craft Magic Arms and Armor feat and if meets the level prerequisites of these abilities: corrosive, corrosive burst, cunning, distance, flaming, flaming burst, frost, greater lucky gun, huntsman, icy burst, lucky gun, reliable gun, seeking, shock, shocking burst, steadfast gun, and thundering. Although the properties duplicate the magical weapon abilities of the same names, the gunslinger can add them through alchemical means or technological engineering. The gunslinger can add these properties to her bonded firearm through the same process as creating magical weapons (see Creating Magical Weapons on page 551 of the Pathfinder Core Rulebook). These abilities can be added to any properties the bonded firearm already has, but duplicate abilities do not stack. Thus, a gunslinger with a bonded pistol must be at least 8th level to add the Reliable Gun magic ability to the pistol (see the Reliable Gun magical weapon property in Ultimate Combat).
If the bonded firearm is broken beyond repair and is not destroyed, it retains all of its bonded firearm properties and can be used to craft a new gun. The magic properties of a bonded firearm, including any magic abilities added to the firearm, only function for the gunslinger who owns it. If a bonded firearm’s owner dies, or the firearm is replaced, the firearm reverts to being an ordinary firearm of the appropriate type.
If a bonded firearm is damaged, it can be restored to full hit points after making the appropriate Craft check and one day of work. If the bonded firearm is lost or destroyed, it can be replaced after 1 week of work and ¼ the cost of crafting a new masterwork firearm. Bonded firearms replaced in this way do not possess any of the additional enchantments of the previous bonded firearm. A gunslinger can designate an existing magical firearm as her bonded firearm. This functions in the same way as replacing a lost or destroyed firearm except that the new magic firearm retains its abilities while gaining the benefits and drawbacks of becoming a bonded firearm.
I liked how Gun Affinity rolled off the tongue vs. Gun Bond or Firearm Bond. Maybe Gunslinger's Bond? Anyways, its just a name, the idea is what matters.
Also, I think, inconjunction with the above changes, and the change to gun training below, this would take care of the general issue of the gunslinger's inability to use full atttacks without using mutiple barrels, tons of guns, or pinholing musket users to using Dead Shot to benefit from their full attacks.
In addition to the gunslinger’s bonus to damage rolls, she greatly improves her reloading skills and speed. Beginning at 6th level, if the gunslinger has Rapid Reload, whenever she uses the Lighting Reload Deed or is using alchemical cartridges (or both), she can reload a single barrel firearm twice per round. At 11th level, the gunslinger can reload a single barrel three times per round, and at 16th level, up to four times per round. Each reloading action occurs as a free action and must be taken either before or after the gunslinger discharges her firearm to allow the gunslinger to make a full-attack action during her turn.