Swapping Animations

So, guys I was kinda trying to swap some weapon animations myself but it seems I just need a teacher now. So here's what happened:

First I converted a weapon model normally.I got this. Let's call it modelA.

So you see most of the the animations weren't working as expected. Luckily, I found a model similar to it having the same animation. The model was this. Let's call it modelB.

The I took Imported the reference model from modelB( with triangles and skeleton) and imported the reference meshes from modelA (only triangles this time). They fit each other perfectly. So, I removed the meshes from modelB (not the skeleton people). I then selected the meshes of the modelA, went to the joint tab, clicked on a bone and clicked "Assign" button. I then clicked on another bone and again clicked the assign button. I did this to the last bone. I then exported the reference model, and compiled it with the animations of modelB. I got this. Let's call it modelC.

So now you can see what's wrong with modelC. Well, if you didn't see it, it's the animations like reload, idle, add silencer, etc.

The Ultimate question is:
HOW DO I FIX THIS?

Solved