Why Cant a Handle Part on a tool Be Animated?

So Im making a gun animation To My Working gun. I know That it should not Be A handle But whats the easiest way and the easiest explaining? Cuz i Really need it.

I made A website On What It should be and The resluts videos

Heres the link: link

If theres anyone who know it please just relpy

Because the handle part is constantly being held in place by the player's hand. To get around this you can set the handle to an invisible part and just connect the rest of the tool to that.