This is Frimenitnet's AKM 7.62 compiled as a replacement to the game's Assault Rifle.
In order to install this, first make a copy of game's dlc.rpf file which can be found in "...\Grand Theft Auto V\update\x64\dlcpacks\patchday3ng" (details can be found here). The reason of using OpenIV's mods folder is to prevent the game to automatically verify game's files.
Once done, replace the original "w_ar_assaultrifle_hi.ydr" and "w_ar_assaultrifle.ytd" with the ones provided in the archive.
Only the highpoly model version is included (as GTA5's modding tools are still not "perfect" and lowpoly models as well as clips at this moment don't really work well with highpoly models).