I'm sure someone brought this up but to reiterate the issue with removing shots and reliability from firearms is what do they have left? Nothing really.
In pathfinder reliability, volley, and power are kind of the metrics by which you measure whether or not a ranged weapon is worth it and these only get worse as you level up and increase your ways of shrugging damage. In games like Call of Cthulhu ancient firearms that fire once a minute and do 1d10 work fine because you've maybe got 18 health max if you are an Adonis of personal health and take weeks to recover from. In pathfinder 4d6+2 (assuming base damage and a +2 for enhancements) is less than the Fireball the sorc can throw about every round if they want or what a Young White dragon can do with just his breath weapon every 1d4 rounds. Neither of those are uncommon, hell the dragon is just 1 over APL for the earliest someone could feasibly afford a +2 weapon following wbl.
In other words if you are going to be taking away attacks per round you need to up the damage to compensate A LOT. If I'm losing a round of attacks and I'm getting two attacks a round and I cannot shorten that the damage needs to be like 4 hits. Hell, I'd actually say closer to maybe 6 since if I miss it's like I've missed all of my attacks for 2 solid rounds. These numbers scale up the more time you're planning to take away from them. Otherwise people just won't use it.
This is why things like the crank crossbow out of RTT or the caltrop spear from Giant Hunters never get used. They are weapons designed to be too expensive both in feats and cash while also being unreliable to ever make you want to invest in them as a character.
Think about these play styles: Switch hitting, skirmishing, and sniping.
Most ranged weapons do a small amount of damage per shot, but make up with it via a large number of shots. Take a longbow for example. At level 10, I would expect to be doing around 1d8 + 4(strength) + 3(enhancement) + 4(class features) = ~15 damage a shot.
Now normally someone who wants to be good at bow will invest in manyshot, rapid shot, precise shot, point blank shot. With this heavy feat investment, you get 3 shots at -2, and one at -7 at level 10. This also means that when you cannot full attack, your damage is quite lack luster.
Now what does a skirmisher/sniper want? They want maximum hit and run/hide potential. To accomplish this, you want something that plays well with vital strike. Taking a full round action to reload isn't a big deal when you are hiding or in cover.
What does a switch hitter want? Something that can be effective without a huge feat investment. A switch hitter could use these firearms without feats and do decent damage until they ran out of loaded weapons.
I personally have different ideas for accomplishing these things than the OP, but those would be my stated goals for similar firearms changes.
TLDR: The current rules and meta in pathfinder focus on rapid firing ranged weapons. Some of us would like to see more options for other builds/ideas to be effective. We can accomplish this by changing the firearms rules.