put this code in fas2_guns.lua

Item.Name = "MC51B Vollmer"

Item.Desc = "A modified variant of the G3A3 machinegun."

Item.Type = "type_weapon"

Item.Model = "models/weapons/w_mc51.mdl"

Item.Weight = 12

Item.Volume = 10

Item.CanDrop = true

Item.DropClass = "fas2_vollmer"

Item.CanEquip = true

Item.Illegal = true

Item.EquipSlot = "PrimaryWeapon"

Item.EquipGiveClass = "fas2_vollmer"

Item.PacOutfit = "mp5_back"

Item.CraftingEntClass = "ent_assembly_table"

Item.CraftingTab = "Weapons"

Item.CraftSkill = "Gun Smithing"

Item.CraftSkillLevel = 12

Item.CraftSkillXP = 1

Item.CraftRecipe = {

    ["Firing Pin"] = 1,

    ["Bolt"] = 2,

    ["Trigger"] = 1,

    ["Stock"] = 2,

    ["Handle Grip"] = 1,

    ["Long Barrel"] = 2,

    ["Lower Receiver"] = 2,

    ["Upper Receiver"] = 3,

}

GM.PacModels:Register( Item.PacOutfit, {

    [1] = {

        ["children"] = {

            [1] = {

                ["children"] = {

                    [1] = {

                        ["children"] = {

                        },

                        ["self"] = {

                            ["Event"] = "weapon_class",

                            ["UniqueID"] = "2859473494",

                            ["Operator"] = "equal",

                            ["ClassName"] = "event",

                            ["Arguments"] = "fas2_vollmer@@1",

                        },

                    },

                },

                ["self"] = {

                    ["Angles"] = Angle(-3.2440683841705, -178.67698669434, -22.848773956299),

                    ["UniqueID"] = "1484483537",

                    ["Position"] = Vector(-1.486930847168, -1.2796630859375, -9.1651153564453),

                    ["EditorExpand"] = true,

                    ["Bone"] = "spine 2",

                    ["Model"] = "models/weapons/w_mc51.mdl",

                    ["ClassName"] = "model",

                },

            },

        },

        ["self"] = {

            ["EditorExpand"] = true,

            ["UniqueID"] = "239303487",

            ["ClassName"] = "group",

            ["Name"] = "my outfit",

            ["Description"] = "add parts to me!",

        },

    },

} )

GM.Inv:RegisterItem( Item )

add this to the bottom of sv_manifest.lua

resource.AddWorkshop( "462119296" )