why does the player get tilted when using this gun Im still making?

So I'm making a gun for my game and for some reason the character gets tilted when using it. What am I doing wrong?

Here is the model: https://www.roblox.com/library/4883435621/M1911-test

Please don't give advice on anything but that because all I need is to know why its happening

You're not supposed to have models in tools. Consider ungrouping the model and weld all the parts. Make sure all the parts have CanCollide off.