Selective fire firearm systems and methods

What is this patent about?

’136 is related to the field of selective fire firearms, specifically those capable of switching between a semi-automatic closed bolt mode and a fully automatic open bolt mode. In traditional automatic weapons, sustained fire can lead to extreme barrel temperatures, creating a significant safety risk where a chambered round may detonate spontaneously due to heat, a phenomenon known as cook off. While open bolt systems mitigate this by keeping the chamber empty until the trigger is pulled, they often lack the precision required for semi-automatic fire. The background context of this invention involves providing a hybrid system that maximizes both accuracy and thermal safety.

The underlying idea behind ’136 is a trigger group architecture that uses a mechanical trigger prop to dynamically alter the trigger’s resting geometry based on the selected firing mode. By physically propping the rear of the trigger during automatic fire, the system ensures the bolt carrier is caught in an open position by a dedicated sear while simultaneously preventing the trigger sear from catching the hammer. This insight allows the firearm to transition from a closed-bolt first shot to a sustained open-bolt cycle, ensuring that the weapon always finishes a burst with an empty, cooling chamber.

The claims of ’136 focus on a trigger group where the trigger itself occupies distinct forward positions depending on whether the weapon is set to fully automatic or semi-automatic operation. The independent claims specify a hardware configuration including a bolt carrier, a hammer with a primary notch, and a trigger prop that selectively blocks the trigger sear from engaging that notch during open bolt cycles. Additionally, the claims protect a safety mechanism involving a selector and an activator button that forces the user to consciously acknowledge the risk of cook off before switching from open bolt to closed bolt operation.

In practice, the invention utilizes a dual-pivot open bolt sear with a wishbone design to manage the high kinetic energy of a returning bolt carrier. When the trigger is released during a burst, the trigger prop slides a foot under the trigger tail, maintaining a specific angle that keeps the open bolt sear raised. The wishbone geometry of the sear allows its legs to flex slightly upon impact with the bolt carrier, dampening the shock and directing forces into the receiver walls rather than a fragile pivot pin, which prevents the sear from oscillating and causing an accidental discharge.

This approach differentiates itself from prior art by integrating a deliberate user-interface hurdle—the risk button—to prevent accidental transitions to a closed-bolt state when the barrel is dangerously hot. Unlike standard selective fire rifles that may fire the first shot of a burst with excessive recoil impulse, this system can be configured to deliver a consistent recoil impulse by ensuring subsequent shots benefit from the forward momentum of the bolt. By combining a propped trigger geometry with a shock-absorbing sear, the invention achieves a level of controllability and thermal safety that traditional closed-bolt or simple open-bolt designs cannot match.