Strange behavior when mixing nifs

[Andyno]

Hello there.

 

I was trying to import the sawed-off barrel mesh to the Point Lookout's Double Barrel Shotgun mesh. Everything looks fine until I started the game. Firing, holding, equiping, and I don't know what else seems to be in order but when it comes to reloading... well look for yourself. This screenshot was made after the reloading process - the shotgun never returns to its original state.

 

 

 

Thanks in advance.

A.