reply to this classmates discussion post This weeks discussion we talk about the different types of blow backs and their similarities and how the contrast with each other. We chose two different variants to discuss and the first one I chose was the Roller Delayed Blow-Back. This operation uses rollers on the side of the bolt carrier moving it backwards the rollers swing outwards into the grooves in the receiver stopping the backwards motion of the bolt head allowing the bolt carrier to move rearward. Being created in the 1940s by Michele and Bartolomeo Ortolani, they used it for a prototype SMG of the design. Not being successful, Germans took the idea and made an early roller system as in experiment for the MG 45 and the STG 45. Later in the 1950s the Germans Heckler and Koch refined it again for the G3 rifle and later on again for the MP5