L4D2 View model problems

No idea if anyone has any experience with L4D2 weapon modding here, but i figured it’s worth asking anyway.

I’m trying to do a simple mod of the original M16 model, but when i use it ingame, the weapon model is nowhere on the screen except for a brief flash of it clipping through the camera when i first pick it up, reload or melee with it, and the camera screws up by slowly tilting and twisting sideways until walking forwards takes me sideways and shooting ends up hiting nowhere near the crosshair untill i switch to a different gun and the view returns to normal.

Here’s what it looks like in idle view and whilst reloading.

I haven’t messed around with the animations or bones or anything, just decompile > modified mesh > recompile, but i’d guess that the problem is with the bones being broken somehow.

Anyone got any ideas what’s causing this?