Roller-Delayed Blowback
Definition
An operating arrangement using roller-related mechanical geometry to regulate breech opening rather than the same positive-locking sequence used in roller-locked systems. The actual design must be identified; the presence of rollers does not establish direct roller impressions on a cartridge shoulder.
Heckler & Koch describes the 9×19 mm MP5 as closed-bolt and roller-delayed. Roller delay is distinct from a simple unlocked-breech description, but the rollers do not thereby contact the cartridge shoulder. Two invented oval impressions are not an MP5 diagnostic signature.
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