To install with OpenIV you replace the provided 
w_sb_compactsmg and mag files in these two places:
 
GtaV\mods\update\x64\dlcpacks\mplowrider\dlc.rpf\x64\models\cdimages\weapons.rpf
GtaV\mods\update\x64\dlcpacks\patchday8ng\dlc.rpf\x64\models\cdimages\weapons.rpf


 Thanks for downloading.