I made a gun for my character, I tried to add a Hand Holder bone to my character rig to be able to move the gun as the characters hand moves. And I parented it in a way that the Hand Holder bone was effecting the gun 100%. but the problem is that the gun mesh is not in the Hand Holders position and it has some offsets :

I researched google for any answer but the only thing I found is by changing the weight of the bones which doesn't worked.

I tried doing weight painting and resetting the position of the gun, and none of them worked for me.

blend file :