When it comes to rifles, most firearms owners are familiar with gas-operated rotating bolts, as it is the most prevalent type of operating mechanism being the heart of an AR-15 and AK-47 (and most other modern semi-automatic weapon systems, for that matter). Few owners are well-versed in the operation of other recoil types.
In modern firearms, one of the rarest types is delayed blowback operating mechanisms like the roller-delayed found in the MP5, CETME, etc. (even though it traces its roots to German WWII engineering efforts in both 8mm Kurz and 8mm Mauser.) Even rarer is the lever-delayed blowback system found in the French standard-issue FAMAS. Delayed blowback, while effective, is often limiting in its band of acceptable loads (too weak will not have enough energy to full operate the mechanism and too powerful rounds will cause premature unlocking).
Given the operating systems relative rarity, I am surprised to see such an excellent tutorial on its operation. A relatively unknown and self-proclaimed “variety channel” MouseGunner has posted up the phenomenal video on the operation of delayed-blowback mechanisms.
The video makes excellent use of cut-aways of various levels to showcase how the two mechanisms work. Roller delayed blowback is showcased in a standard MP5 sub-machine gun and lever-delayed blow-back is showcased in a FAMAS rifle. The FAMAS is particularly interesting given its oddity, which the video does explain why there is the little “hump” on the back of the stock (hint, its related to ejection).