Creating animations for different types of weapons

Hello! Tell me, I have animations purchased in the marketplace (MoCap), specifically in the hands of an automatic rifle (runs, jumps, and others).
I need to make a shotgun out of this animation. I have to put a shotgun in his hand and change the position of my left hand … and so on each animation (and I have 305 of them).

So the question is … is there any way to automate this process or how to bind the position of the hands for different types of weapons?

Sorry for my bad English (using Google translate)