I think this is a question more for the game mechanics thread. You should, however, be able to fire a crossbow more than once with the Crossbow Expert feat.
There are two weapon properties at play here - Ammunition and Loading.
Ammunition. You can use a weapon that has the ammunition property to make a ranged attack only if you have ammunition to fire from the weapon. Each time you attack with the weapon, you expend one piece of ammunition. Drawing the ammunition from a quiver, case, or other container is part of the attack. At the end of the battle, you can recover half your expended ammunition by taking a minute to search the battlefield.
You need one hand for the weapon and one for the ammunition, preventing you from holding a shield or second weapon. For two-handed weapons, the second hand involved in firing the weapon can also be used in the loading process.
Loading. Because of the time required to load this weapon, you can fire only one piece of ammunition from it when you use an action, bonus action, or reaction to fire it, regardless of the number of attacks you can normally make.
This property (not Ammunition) restricts the rate of fire. This is also the property that Crossbow Expert removes:
You ignore the loading property of crossbows with which you are proficient.
I know its been touched before but why cant I have a lvl 20 fighter that can take 4 heavy crossbow attacks with crossbow expert?
I think this is a question more for the game mechanics thread. You should, however, be able to fire a crossbow more than once with the Crossbow Expert feat.
There are two weapon properties at play here - Ammunition and Loading.
Ammunition. You can use a weapon that has the ammunition property to make a ranged attack only if you have ammunition to fire from the weapon. Each time you attack with the weapon, you expend one piece of ammunition. Drawing the ammunition from a quiver, case, or other container is part of the attack. At the end of the battle, you can recover half your expended ammunition by taking a minute to search the battlefield.
You need one hand for the weapon and one for the ammunition, preventing you from holding a shield or second weapon. For two-handed weapons, the second hand involved in firing the weapon can also be used in the loading process.
Loading. Because of the time required to load this weapon, you can fire only one piece of ammunition from it when you use an action, bonus action, or reaction to fire it, regardless of the number of attacks you can normally make.
This property (not Ammunition) restricts the rate of fire. This is also the property that Crossbow Expert removes:
You ignore the loading property of crossbows with which you are proficient.
You CAN have a level 20 fighter that can take four heavy crossbow attacks with crossbow expert.