The MR920 accommodates Gen4 Glock recoil assemblies, but includes Shadow System's own modified Gen3 recoil system. This single spring system is user adjustable for those wishing to tune the gun with different spring weights. The included spring is a conventional weight flat wire spring but is manufactured from higher-quality chrome silicon material.All internal slide parts are machined from billet stainless steel. The extractor is Shadow Systems own high-reliability enhanced LCI extractor. The LCI features a serration that increases the sensation of the LCI protruding from the slide when checking by feel in darkness. The extractor features Shadow Systems proprietary geometry and material selection to enhance longevity and extraction of a wide range of ammunition.The MR920 pistol includes two magpul 15 round magazines. We are partial to these magazines for several reasons. Aside from their performance in multi-thousand round testing, we appreciate the oversized, serrated basepad which aids in emergency magazine removal particularly with the add-on magazine well installed. These magazines are also substantially easier to disassemble and clean when compared to other designs on the market compatible with our pistol. We view magazine maintenance as a critical aspect of maintaining system reliability. MR920 pistol owners will also benefit from broad magazine interchangeability with Glock-compatible systems.