Wisdom Based Shooting (5e Variant Rule)
From D&D Wiki
Wisdom Based Shooting
Good old guns. Bullet slinging machines that tear through kobolds faster than a wizard on drugs. The only problem is how they're handled in 5e. See, when you flip to page 268 of the DMG, you find yourself with another arsenal of weapons at your disposal. Revolvers, Shotguns, and Laser Rifles; it’s all here. “Sweet” you say to yourself as you try them out in your awesome Fallout 4 campaign. Your adventurers, starting off at relatively low levels haven’t gotten extra attacks at this point. And you begin to realize, “I think it may just be a little bit possible to shoot more than one bullet in a 6 second turn”.
Pesky Kobolds dodging your bullets? Trying to figure out how to line up a dragon relative to your position? Boy, have I got a treat for you! Ladies and gents, I present you Wisdom Based Shooting! Just add your positive Wisdom Modifier by one, and take the resulted numbers amount of shots at the enemy! Sequilitis references aside, this actually is a pretty good idea. While the assault rifle has burst fire and that’s pretty cool, it doesn’t make up for the fact that the only reason anyone uses guns is because they do way more damage than the strongest of Martial Weapons.
Basically, Wisdom Based Shooting, or WBS, lets you shoot a gun up to your wisdom modifier +1 (unless your modifier is negative). If you use WBS on your turn, you cannot use any extra attacks you have. If you use the burst fire property on your turn, you cannot use WBS on the same turn.