- Madbull 12" mk12 rail - Madbull 12.5" outer barrel - Could include 318mm 6.03 prommy inner barrel for an extra $20 - Metal upper and lower receiver ($0) - Lancer tactical gearbox with no motor free of charge ($0) - Polymer retractable stock and motor guard ($0) - It’s got a hop up in there use at your own risk ($0) Basically this was a terrible attempt at a m4 build that had a combined $200 of content inside the rail and then approximately 7 cents on everything else.