Bolt assembly for firearm

A modular bolt assembly system for a firearm with blowback operating system comprising:

• a longitudinal axis;
• a first front bolt piece having a first mass and internally comprising a first longitudinal passage coaxial with the longitudinal axis, the first longitudinal passage being configured to receive a rear portion of a first firearm barrel chambered for a first cartridge;
• a second front bolt piece having a second mass different than the first mass, the second front bolt piece internally comprising a second longitudinal passage coaxial with the longitudinal axis, the second longitudinal passage being configured to receive a rear portion of a second firearm barrel chambered for a second cartridge having a propellant powder charge with energy different than the first cartridge;
• a rear bolt piece internally comprising a third longitudinal passage coaxial with the longitudinal axis, the third longitudinal passage comprising a breech face and being configured to receive the rear portions of the first or second firearm barrel;
• wherein the first and second front bolt pieces each have a common first coupling interface configured to mate with a corresponding complementary configured second coupling interface formed on the rear bolt piece;
• wherein the rear bolt piece is detachably coupleable to the first or second front bolt piece to form a mechanical interlock which prevents separation thereof in a direction along the longitudinal axis.