I'm the DM of a 5e campaign and have a 5th level Fighter with a heavy crossbow.
He has the crossbow expert feat, and at 5th level has extra attack feature. Using crossbow expert he is able to reload and fire his crossbow twice a turn. He's also got the sharpshooter feat, so he can take a -5 to attack roll—if it hits +10 damage. And a high dex (+3 at 5th level).
He is able to do 1d10 +3 + 10 with sharpshooter = around 17-20 damage per shot. And with extra attack he can now do 17-20 damage twice per turn. That's roughly 34-40 damage per turn.
He also has a bonus action that allows him to make one more attack. (3 attacks per round) That he uses sharpshooter with, and so, does an additional 17-20 damage. He also can add in superiority dice to add to his attack roll with precision attack (1d8 to his attack roll). He has a limited amount of those, but this seems extremely over powered with a heavy crossbow that probably weighs in the neighborhood of 40-50 pounds and is two handed. I know these are heroes but with the bonus action of one more attack, that's literally reloading a heavy crossbow bolt of a heavy crossbow every 2 seconds. He's dexterous, but, that doesn't make him a machine gun.
How would you scale this back if you were the DM? My thought is why be a Fighter with extra attack if you can't fire a heavy crossbow twice, at the same time…this seems insane. I don't want him to have to rebuild his character.
Thoughts, anything in the rules that I'm missing?
I agree, the feats do not add the "third attack". No doubt about it. I need to look at his character sheet, going off of memory here. But, I believe one of the "fighter" (not sure what archetype of fighter) provides him an extra attack or bonus action. He can't attack twice using the bonus action, but has used it to make one more attack. This is limited to so many times per short rest or per day (again not very helpful since I don't have the exact ability in front of me.)
So, with the two attacks he gets as a fighter, can he switch targets with those attacks. Nothing really stated about that. I've let him switch targets, but question if that's appropriate since it's part of the same attack.