The Valken SMAG 140rd mid-cap airsoft magazine is constructed of durable hard polymer material, are lightweight, and can take a beating. The 6mm AEG magazine features a standard STANAG design making it great for all types of M4 magazine pouches, and compatible with most major brand M4 airsoft electric guns. They include a stronger feed spring allowing up to 0.36g BBs to feed flawlessly, and no winding is required like hi-cap magazines. An airsoft speedloader is required to load BBs into these magazines (which is not included). We recommend our Valken speed loaders for use with the SMAG airsoft gun magazines.