This item is not included in any spawn asset, but it doesn't necessarily mean that it doesn't spawn naturally on any of the maps.
CA_Winchester_10.dat
GUID 84eaa0ffe9404391866ed41849d538d7
Type Magazine
Rarity Epic
ID 4033
Size_X 1
Size_Y 2
Amount 10
Count_Min 7
Count_Max 10
Calibers 1
Caliber_0 4101
Tracer 4145
Blueprints 4
// Box, Crate
Blueprint_0_Type Ammo
Blueprint_0_Supplies 1
Blueprint_0_Supply_0_ID 4149
Blueprint_0_Build 4180
Blueprint_1_Type Ammo
Blueprint_1_Supplies 1
Blueprint_1_Supply_0_ID 4150
Blueprint_1_Build 4180
// Winchester 5
Blueprint_2_Type Ammo
Blueprint_2_Supplies 1
Blueprint_2_Supply_0_ID 4010
Blueprint_2_Build 4180
// Winchester 10
Blueprint_3_Type Ammo
Blueprint_3_Supplies 1
Blueprint_3_Supply_0_ID 4033
Blueprint_3_Build 4180