Inven FRM fixes/adjustments

[NovaRain]

[Minor bug] Patched a hole in sniper rifle's stock:

[Aesthetic] Adjusted the barrel angle of Mauser pistol. It always looked slightly off (bent upwards):

[Aesthetic] Adjusted hunting rifle's grip. It looked bent sideways to me, kinda awkward even for a rifle in a post-apocalyptic setting:

[burner1024]

Thanks.