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. What changed with the gen 3 magazine? We made the following improvements: US-based manufacturer. Modular tooling. Raised ribs on the back of the magazine allows these to fully match the OEM magazine position in the mag well, which should eliminate any tolerance stacking that results from Glock frame variations.