GTA V modding (attempt) - help pls

So, I've decided to start modding V, even if my PC can barely handle it. I decided to make something easy for start, but it wasn't so easy at all. I made a replacement (addon in near future) for assault rifle - wz.96 Beryl. Everything works fine (I think so) except for the bug showed in the video.

So could anyone help me? The request is mainly directed to SkylineGTRFreak, FightingFalcon or other GTA V modders that know the drill ^^