Design Summary, Hammer Buffer

BACKGROUND

The firearm from which this invention was created was originally designed and produced in 1957; The CETME Model A. It was later procured, updated, and manufactured by the German Company Heckler & Koch, with the most famous variants being the G3 and MP5. The G3 in particular was utilized world-wide, and is the third most produced firearm in history.

Although these firearms have decades of proven effectiveness, there have been inherent design drawbacks since the original prototypes. The most notable being the lack of “fine tuning” of the firing cycle, and poor ergonomics/performance from the trigger mechanism. These drawbacks however contained the inspiration and part of the solution to both issues. It is unknown how  much the original designers recognized the mechanics at play, if at all. It is clear that they were never pursued further by either parent company, and the designs themselves have faded into obsolescence.

PROBLEM STATEMENT AND ORIGINAL CONCEPT

Roller Delayed Blowback Firing Cycle

Roller Delayed Blowback Firing Cycle

The operating principle for these firearms is called Roller delayed blowback. When the round is fired, the rollers engage and momentarily halt the rearward travel of the bolt group; reducing recoil and improving ballistic performance. The timing for this operation is controlled solely by the locking piece, shown above in red, which dictates how long the bolt remains closed. Any changes due to barrel length, silencer use, or ammunition loading require replacing the locking piece, and even then rarely achieve optimum dwell time.

Trigger Pack Schematic

Trigger Pack Schematic

The original trigger assembly was incredibly robust, utilized in countless variants, but tragically over complicated. The trigger’s pull length and weight are exorbitant, hampering marksmanship. The previously unseen principle is that the trigger assembly performs more than one function, and its poor performance was due to a compromise between the two rolls.

With a few exceptions, none of the firearms based off the CETME’s original concept utilized a buffer spring to reduce rearward force from the bolt carrier group. While there are other design features that assist in buffering, the trigger assembly is the primary buffering component; by storing the kinetic energy in the trigger springs, and its skewed axis relative to the movement, momentum is reduced, and the returning bolt carrier group is therefore slowed.  The release of this energy is what gave the system its heavy pull weight and poor overall usability.

OVERVIEW

The entire trigger group has been replaced by a single unit, which houses the trigger mechanism, fire control group, hammer buffer, and also functions as the grip interface for the user. The ejector, is the only remaining component from the original design, and his attached in the same location relative to the firearm.

Hammer Buffer Top View

Hammer Buffer Top View

The trigger and fire control group has been replaced with commercially available, off the shelf components originally utilized in AR-15 style rifles.

AR-15 Trigger, Hammer Assembly

AR-15 Trigger & Hammer Assembly

 

Ratchet Style Buffer

Ratchet Style Buffer

 

Ratchet Buffer Schematic

Ratchet Buffer Schematic

The hammer buffer can be utilized in conjunction with the hammer (above), or can be an independent assembly, based on space limitations and performance required (below.)

Independent Buffer Configuration

Independent Buffer Configuration

In either configuration, the basic principle of the hammer buffer remains the same. As the bolt carrier group travels to the rear, the momentum is stored in the buffer’s springs, and dissipated off-axis by friction against the bolt.

Once the bolt carrier group has been satisfactorily dampened, contact between the carrier and the buffer is halted, or the return path is achieved, which allows the spring to release return to its unloaded state without transferring that energy to the forward moving bolt (configuration dependent.)

With this system in place, dwell time, rate of fire, and overall cycle time can be changed in the firearm by adjusting the hammer buffer. In addition to altering spring lengths and force constants, pre-load, load, and maximum deformation rates can be easily changed by placing a control on the side of the lower housing. Additionally, changing the line of action for the buffer in either configuration allows for non-linear dampening behavior by converting part of the bolts momentum into tangential forces.

While this system was originally designed to address issues in roller delayed blow back firearms, minimal changes to existing rifle designs can easily allow the hammer buffer concept to be utilized in a variety of firearms; replacing buffer tube extensions and providing more methods to optimally tune a firearm.