Just a straight reskin of crossbows, hand for pistols, heavy for rifles. The player is pushing to at least have an "armor penetration" property that allows the weapon to ignore 1 AC (a roll of 14 hits an enemy with 15 AC, for example). I don't really like this, I understand the logic, but I feel like that could be applied to many weapons? What do you guys think?
Without getting into the arguments all over the interwebs about what bullets will/can penetrate medieval armors the short answer is, many of the common ammunition would be able to pierce them just fine. That said, there were also specifically designed arrow heads made to pierce the same armors and they were successful to varying degrees.
Unless you wanted to get that detailed on ammunition types, I don't see a problem with leaving AC alone and forgoing the "penetration" bonus.
When it comes to AC and hitting on a miss I either rule that the shot doesn't penetrate, or they flat out miss, so to let him hit on a 14 against an ac of 15 would have nothing to do with a bullet, that is the player not thinking about the mechanics of the game.
You could rule bullets from a gun overcome bludgeoning resistance or something, that would make more sense.
I have some guns in my campaign and pretty much just run them straight forward as far as to hit and dmg, go with them breaking on rolls of 1s or 2s and taking an action to load.
My rifles for exampled do 2d10 damage but it takes a round basically to reload them, so the damage output is mitigated.
Who will have access to guns in your campaign? Is this just a single character or will other characters be using them also? Are they being used by armies in the world extensively, or are they new? Depending on the answer to these questions, you might want to rule differently on their effectiveness.
Early guns still had trouble piercing plate armor (more broadly, heavy armor in D&D), but your player might have a point when it comes to light and medium armor. It's true that other weapons are "armor piercing," but when guns emerged, they led to an absolute paradigm shift in warfare in part because of their effectiveness against all types of fortifications. So another thing to consider if you're allowing handguns is how the world is impacted by cannons, which if anything are much more disruptive.
I'd suggest going with the firearms from the DMG, as Grizzlebub suggested. This way, you can say their more effective damage compared to similarly-sized crossbows already represents their "armor-piercing" nature. I don't think the higher damage (1d10 for pistols, 1d12 for muskets) is going to break your game. Depending on your specific campaign, you might also want to consider the expense and hassle of maintaining guns and dealing with gunpowder, though I wouldn't overdo this.
If you want to be generous, you could also create some better guns, let's call them "masterwork," that are very effective at piercing armor. These might give a +1 bonus to attack (and maybe damage) rolls against targets wearing no armor, light armor, and perhaps medium armor. This seems like a reasonable compromise, and it could give the character something to seek out in their adventures.
Just a straight reskin of crossbows, hand for pistols, heavy for rifles. The player is pushing to at least have an "armor penetration" property that allows the weapon to ignore 1 AC (a roll of 14 hits an enemy with 15 AC, for example). I don't really like this, I understand the logic, but I feel like that could be applied to many weapons? What do you guys think?
Without getting into the arguments all over the interwebs about what bullets will/can penetrate medieval armors the short answer is, many of the common ammunition would be able to pierce them just fine. That said, there were also specifically designed arrow heads made to pierce the same armors and they were successful to varying degrees.
Unless you wanted to get that detailed on ammunition types, I don't see a problem with leaving AC alone and forgoing the "penetration" bonus.
The Dungeon Master's Guide has a decent section on firearms that you could use as a guide, if you are interested.
When it comes to AC and hitting on a miss I either rule that the shot doesn't penetrate, or they flat out miss, so to let him hit on a 14 against an ac of 15 would have nothing to do with a bullet, that is the player not thinking about the mechanics of the game.
You could rule bullets from a gun overcome bludgeoning resistance or something, that would make more sense.
I have some guns in my campaign and pretty much just run them straight forward as far as to hit and dmg, go with them breaking on rolls of 1s or 2s and taking an action to load.
My rifles for exampled do 2d10 damage but it takes a round basically to reload them, so the damage output is mitigated.
Who will have access to guns in your campaign? Is this just a single character or will other characters be using them also? Are they being used by armies in the world extensively, or are they new? Depending on the answer to these questions, you might want to rule differently on their effectiveness.
Early guns still had trouble piercing plate armor (more broadly, heavy armor in D&D), but your player might have a point when it comes to light and medium armor. It's true that other weapons are "armor piercing," but when guns emerged, they led to an absolute paradigm shift in warfare in part because of their effectiveness against all types of fortifications. So another thing to consider if you're allowing handguns is how the world is impacted by cannons, which if anything are much more disruptive.
I'd suggest going with the firearms from the DMG, as Grizzlebub suggested. This way, you can say their more effective damage compared to similarly-sized crossbows already represents their "armor-piercing" nature. I don't think the higher damage (1d10 for pistols, 1d12 for muskets) is going to break your game. Depending on your specific campaign, you might also want to consider the expense and hassle of maintaining guns and dealing with gunpowder, though I wouldn't overdo this.
If you want to be generous, you could also create some better guns, let's call them "masterwork," that are very effective at piercing armor. These might give a +1 bonus to attack (and maybe damage) rolls against targets wearing no armor, light armor, and perhaps medium armor. This seems like a reasonable compromise, and it could give the character something to seek out in their adventures.
I didn't realize that the game had gun mechanics already built in. I'm perfectly happy with those options. Sorry for the spam thread!