Parameters and Values

First of all, set all values in the WeaponControllers script - Effects, Sounds, Attacks parameters, etc.

Points and Colliders

In this step, you should adjust the weapon collider.

Then, go to the weapon prefab and adjust the position of "AttackSpawnPoint", "ShellSpawnPoint", "AttackCollider" (depending on an attack in the weapon).

*if you're using the Unity version up to the 2018.3, you should place the prefab in a scene, adjust it, then apply changes.

Attack and Shell Points


Then adjust the character's hands and the weapon position/rotation in them: