363mm. For most standard M4/M16 and variants. Full metal barrel. Full metal hopup. Totally working. AEG. No use for it. Incredibly tight. The hopup is nearly stuck on and is super hard to take off. Comes with all working parts, just slide it in your rifle and shoot! $25 plus shipping. Price isn't really negotiable. Not too many things I'd like to trade for. Cash is king!