You'll have to forgive me in advance if this idea seems a little scattered at first. But here we go!
So I started thinking today as I was drinking my hypothetical cup of tea with my fancy monocle mustache - as I usually do, I should mention - about something this game lacks. And that, ladies and other fancy monocle'd gentlemen who may or may not have mustaches as manly as mine, is this:
Shotguns.
Yes, I said it - SK requires shotguns. I mean, think about it. We have handguns. We have SMGs essentially. We've got guns that even put Knights flat on their rear from the recoil in some cases. So why not a shotgun line? In the end, I don't feel like it would be too overpowered with some of the concepts listed below, since good gunslingers (who don't let enemies get close) wouldn't have a very strong need for it, and other players wouldn't necessarily want this gun unless they had ideas in mind for how to use it.
The physics would work like this - the closer you are to your target, the more damage you inflict, since more pellets would enter into the target. So in that manner, each pellet would have a damage value, with the idea of every pellet hitting yielding the highest damage potential.
As far as range and utility is concerned, I feel that a 3-4 block range is adequate for a shotgun to be relatively effective (3 blocks guaranteeing 100% damage is inflicted, with a drop off to about 75% for 4 blocks away, and have a steep drop off from there on out). The knockback from the shotgun should be relatively high, but require a reload after every shot, with the reload animation being slightly slower than your typical reload for a gun.
The charge attack could be a stronger shot but take a while to charge (maybe the amount of time to charge the Gran Faust, or 75% of that ideally but yeah, this is also to prevent abuse). Charge attack effects would be stronger knockback, a 1.5x damage multiplier per pellet hit, and at higher upgrade levels, High Chance of (Enter Status Here).
Yes, you did read that paragraph correctly as well - one shot = one reload, regardless of who uses it. This would be in order to prevent over-use in certain situations and cornering large masses of enemies with a semi-automatic shotgun. While the concept is cool, in practice it would probably break the game to the point that no one would want to use anything else.
As far as actual gun design goes, I feel that a sawed-off shotgun being used as the base design would work great. It's got a break stock that would allow the gun to be reloaded from the back and rechambering the shotgun shell into the barrel. Imagine a double-barrel shotgun and how it reloads, and there you go.
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Potential benefits of the shotgun line, if implemented - Gunners would not be as restricted in their close-range options. Realistically, gunners don't have much of an answer to mobs except to shield bash and hope there's an opening to walk out afterwards. On top of that, while gunners have a solid line of armors (although their armor EFFECTS could use a nice buff or a new line to round out some of where it's lacking), I still feel like the gunslingers in general need more answers to deal with various threats without deviating from their class structure, in a sense. Conceptually, the strong knockback would make it a close-range option for those who get cornered in general, not just gunslingers, thus allowing for smarter players to use the shotgun to free themselves and shield bash an additional enemy for more breathing room. Hey, it might seem like an overpowered option here, but they're already throwing knockback onto energy revives in the testing server tomorrow, so apparently this is a feasible option too.
Potential problems of the shotgun line, if implemented - Bad gunners who don't know what they're doing with it would run in and essentially kill themselves because they think they have the best of both worlds now. Might otherwise give too much of a boon to gunslingers that otherwise don't have a reason to run into a fight unless they solo a lot, and even then the shotgun's purpose would largely be negated if a gunslinger just doesn't let themselves get cornered.
I'll take ten.