Great mod. One of the best weapons mod. If anybody is using Better barracks mod and want to use this awesome mod do this:
1. download this mod + long War Smg pack (you won´t see these weapons in loadout screen, it´s only for this mod to work)
2. download A Better Barracks: Custom Weapons Support
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1162417893&searchtext=BARRACK for xustom weapons for Better Barracks mod
3. put these lines to XComCustomWeaponsSupport.ini in A Better Barracks: Custom Weapons Support:

+CustomWeapons=SCAR_MJ_CV
+CustomWeapons=SCAR_MJ_MG
+CustomWeapons=SCAR_MJ_BM
+CustomWeapons=Bull_MJ_MG
+CustomWeapons=Bull_MJ_CV
+CustomWeapons=Bull_MJ_BM
+CustomWeapons=SR_MJ_CV
+CustomWeapons=SR_MJ_MG
+CustomWeapons=SR_MJ_BM
+CustomWeapons=CAR_MJ_CV
+CustomWeapons=CAR_MJ_MG
+CustomWeapons=CAR_MJ_BM
+CustomWeapons=MCAR_MJ_CV
+CustomWeapons=MCAR_MJ_MG
+CustomWeapons=MCAR_MJ_BM
+CustomWeapons=ARES_MJ_CV
+CustomWeapons=ARES_MJ_MG
+CustomWeapons=ARES_MJ_BM
+CustomWeapons=AR_MJ_CV
+CustomWeapons=AR_MJ_MG
+CustomWeapons=AR_MJ_BM
+CustomWeapons=Carbine_MJ_BM
+CustomWeapons=Carbine_MJ_MG
+CustomWeapons=Carbine_MJ_CV
+CustomWeapons=Reaper_MJ_CV
+CustomWeapons=Reaper_MJ_MG
+CustomWeapons=Reaper_MJ_BM
+CustomWeapons=BR_MJ_BM
+CustomWeapons=BR_MJ_MG
+CustomWeapons=BR_MJ_CV
+CustomWeapons=MBR_MJ_CV
+CustomWeapons=MBR_MJ_MG
+CustomWeapons=MBR_MJ_BM
+CustomWeapons=SG_MJ_CV
+CustomWeapons=SG_MJ_MG
+CustomWeapons=SG_MJ_BM
+CustomWeapons=XD_MJ_CV
+CustomWeapons=XD_MJ_MG
+CustomWeapons=XD_MJ_BM
+CustomWeapons=MINI_ME_CV
+CustomWeapons=MINI_ME_MG
+CustomWeapons=MINI_ME_BM
+CustomWeapons=LMG_MJ_CV
+CustomWeapons=LMG_MJ_MG
+CustomWeapons=LMG_MJ_BM
+CustomWeapons=MMG_MJ_CV
+CustomWeapons=MMG_MJ_MG
+CustomWeapons=MMG_MJ_BM
+CustomWeapons=XDef_Mk_CV
+CustomWeapons=XDef_Mk_MG
+CustomWeapons=XDef_Mk_BM

Profit.