Firearm with reciprocating bolt assembly

What is this patent about?

’076 is related to the field of semiautomatic firearms, specifically cycling mechanisms for high-power necked rimfire cartridges. Traditional blowback systems often rely on bolt mass to delay opening, which is frequently insufficient for the higher pressures of modern rimfire rounds like the .17 WSM, leading to reliability issues or dangerous out-of-battery firing. The invention addresses the need for a mechanically simple yet robust system that provides both a positive mechanical delay and a redundant safety lockout for the firing pin.

The underlying idea behind ’076 is the use of a single, multi-functional floating blocking member that simultaneously acts as a mechanical lock and a firing pin safety. By utilizing a transverse-moving component that must be forced inward to allow the bolt to retreat, the system creates a mechanical disadvantage that delays blowback. This movement is coupled with a geometry-based lockout where the firing pin is physically obstructed by the blocking member unless the bolt is fully seated in the battery position.

The claims of ’076 focus on a bolt assembly featuring a movable blocking member that translates transversely to the bolt's travel axis, controlled by a reverse cam mechanism. Independent claims 1, 8, and 12 describe a ramped carrier within the bolt body that is biased by a spring to push the blocking member into a receiver recess. The firing pin passes through an aperture in this blocking member, which has a variable geometry—specifically a reduced-size region—that physically prevents the firing pin from reaching the cartridge unless the member is fully extended into its locked position.

In practice, the system operates through a dual-cam interaction. When the firearm is in battery, the spring-loaded ramp forces the blocking member upward into a recess in the receiver ceiling, aligning a larger opening with the firing pin to allow ignition. Upon firing, the rearward pressure on the bolt forces the blocking member against an inclined transition surface in the receiver. This creates a reverse camming action where the member must push the internal ramped carrier backward against the heavy recoil spring to retract, effectively multiplying the resistance and delaying the bolt's opening until pressures have dropped.

This approach differentiates itself from prior art by eliminating the need for complex gas-operated pistons or excessively heavy bolts. By integrating the firing pin safety directly into the locking lug, the invention ensures that the firing pin is mechanically isolated from the hammer or the cartridge whenever the bolt is even slightly out of battery. The use of a floating member without fixed pivot pins further reduces wear and sensitivity to fouling, providing a reliable solution for high-pressure rimfire platforms that typically struggle with traditional blowback designs.