That's a world model problem, normally gmod has its own fixed css weapon worldmodels that can be used on npcs (or hl2-like playermodels), but for some reason it seems your game is loading non-fixed versions, it may be caused by an addon or maybe for some reason gmod decided to give priority to the original css worldmodel.
cs: dih
Hehe pp gun
Best thing I could recommend is Advanced Bonemerge Tool And then move it to the arms
That's a world model problem, normally gmod has its own fixed css weapon worldmodels that can be used on npcs (or hl2-like playermodels), but for some reason it seems your game is loading non-fixed versions, it may be caused by an addon or maybe for some reason gmod decided to give priority to the original css worldmodel.