The S15 magazine is a patent-pending” flush-fitting 15 round magazine for the Glock 43X and Glock 48. The S15 is a steel magazine” and is the same length as the OEM Glock 10 round magazine” but holds an additional 5 rounds. Glock pistols and magazines are known for reliability – the S15 maintains that same Glock reliability” while giving you a 50 percent increase in magazine capacity in the same overall footprint. Shield Arms accomplished this increased capacity with their patent-pending magazine geometry” allowing the rounds to stagger” thereby fitting more in the same amount of space. Proudly made in the USA. What changed with the gen 3 magazine? The following improvements: New US-based manufacturer. Modular tooling” allowing Shield Arms to make the S15 and S10 magazines simultaneously. Raised ribs on the back of the magazine allows to fully match the OEM magazine position in the mag well” which should eliminate any tolerance stacking that results from Glock frame variations. New steel” new coating” new heat treat process – new steel is slightly thicker” tougher” and now comes with a new standard black nitrocarburized QPQ finish for a high degree of corrosion resistance