Loading
Limits firing to one shot per action/bonus action/reaction regardless of [[compendium:feat:Extra Attack]]. Crossbow Expert feat removes this restriction.
Loading (Weapon Property)
A weapon with the loading property takes time to reload, limiting how many times you can fire it per turn.
Mechanical effect: Because of the time required to load this weapon, you can fire only one piece of ammunition per action, bonus action, or reaction, regardless of the number of attacks you can normally make.
Impact on Extra Attack: A Fighter with Extra Attack at level 5 normally makes two attacks per action. With a heavy crossbow (loading property), they can only fire once per action unless they have the Crossbow Expert feat.
Loading weapons in the SRD:
Crossbow Expert feat: This feat ignores the loading property of crossbows you are proficient with, allowing full use of Extra Attack with crossbows. It also eliminates disadvantage on ranged attacks within 5 feet and allows a bonus action attack with a hand crossbow after attacking with a one-handed weapon.
Bows vs. crossbows: Bows do not have the loading property. A longbow or shortbow can make multiple attacks per action without any feat. This is a significant advantage for bow users at level 5+, balanced by crossbows dealing slightly higher damage per shot.