The armalites/416's are NBB. Theyre kinda like a shit version of Madbull's drop in CO2 gearbox that fits in an AEG body, but instead of putting the CO2 cartridge in a good spot like madbull's spot in the grip they put it in the mag well meaning you'll have to buy new mags (madbull's you can use AEG mags still). That and Madbull's drop in IS blowback unlike SRC's design.