M500 Shotgun extractor
PPT M500/M590 Maintenance
PPT Preliminary Marksmanship Instruction M500
PS Magazine Article on Shotgun Safety
TACOM LCMC MA 16-011, OBSOLETE SHOTGUN TURN-IN Subject: Maintenance Action (MA) Message, TACOM Life Cycle Management Command, (TACOM LCMC) Control No. MA 16-011, (Informational),Obsolete Shotgun Turn-In
M26 MASS Modular Accessory Shotgun System (MASS) New Equipment training
M26 MASS POI and Lesson Plans
Warrior University 
Training and Educational Material