High quality internal components imported from Japan Japanese-made heat-treated internal spring for excellent feeding and reliability No rewind is needed. One full wind up will allow you to fire the entire reservoir of BBs High strength polymer outer casing takes a beating and keeps on going High strength injection-molded polymer internal casing and feed lip The APS U-Mag is made of high strength POM polymer providing great durability in tough situations. This 300rd magazine is made with internal components imported from Japan what produce extremely smooth loading of the BB, which in practical terms means no re-wind is necessary after one full wind up. Simply give the magazine a full wind and it will last the whole 300rd reservoir.