"Flapper Locking" Makes A Comeback in AA .338 Lapua

@Zapp Brannigan There is this crazy myth that DI is more accurate. As long the barrel is high quality, free floating and the bolt locks well, the gun will be accurate be it shorts stroke, long stroke, DI or delayed blowback.

@Vitor Roma One can make any semi-auto rifle into a tackdriver, just that it's a bit easier (aka cheaper) to do that with the AR's direct impingement than other designs.

@Zapp Brannigan With roller delayed blowback you get full free floating barrel...

@Zapp Brannigan Actually the AR makes a very poor starting point if one wishes to create a semi automatic weapon in 338 Lapua caliber.

We initially considered this approach as it is an obvious one and even went as far as testing several designs based upon this concept. The results clearly indicated that the configuration was less than optimum. Familiarity in this instance is a disadvantage

With the 338 one has to contain the pressure, support the cantilever of the barrel, constrain the recoil of the cartridge as it pertains to leverage on the barrel and match the weapon timing to unlock the breach. To be effective as a semi automatic weapon the system requires stability such that the shooter can effectively observe the fall of shot and at minimum not loose target designation. The heat management of such a system with the requirement to shoot multiple rounds is the last requirement.

So a solid barrel foundation is an absolute given. With a reasonably heavy profile 27" barrel to deal with heat build up, it is problematic to mate with a light alloy receiver and provide contact stresses that are low enough for a minimum 5000 round duty cycle. This is not to say impossible but the size of the trunnion or barrel extension becomes excessive, or the system runs the risk of shooting loose. Working pressures also drive trunnion size. So the expedient route is to fit the barrel directly to a steel receiver suitable to absorb the recoil, heat, and contact stresses. It then makes more sense to lock the breach to the receiver directly and not incorporate a superfluous component.

To time the weapon correctly the extraction cycle must be set to allow the chamber pressure to fall to very low levels before unlock. This dictates that the gas is drawn further down the barrel and then acts upon a large area piston as there is less pressure and duration to provide the necessary energy for cycling. Benefits are that the system is extremely accurate as the mechanism movement has minimal effect on the firing event and the support for reciprocation is now 22" long. Clearances between parts may be relaxed without incurring detrimental angular deviations. A cyclic rate of 450/500 rpm is typical.

Removing the rotating bolt head with locking lugs to disengage the barrel extension saves nearly 1" of overall length and 2" of movement that must be in addition to the length of the cartridge. The savings translate to weight savings and allow the movement to be substantial behind the magazine. The system can now be set as a constant recoil as a variation in the bolt position at the rearmost part of any cycle is well behind the next cartridge from the magazine.

Admittedly we were nervous of such a mechanical deviation from the norm and invested considerably before making these steps. Even so the potential still existed for the rifles to shoot badly or for the variation between weapons to be unacceptable in a production environment. This required that the trial fleet be a larger sample set than normal and that the initial production be closely monitored. We expended somewhere in the order of $175k in ammunition alone before the design was proven.

The rifle has shown a very good tolerance to a production route without introducing stringent tolerance requirements, or unit to unit variations. The design targets for accuracy and durability are exceeded. The typical production unit will report 1/2 moa or better with Black Hills ammunition.

PIP formed part of the weapon design process as did life cycle analysis and FMEA. We have ongoing projects to examine both weight and accuracy of the system as well as operating enhancements to reduce any cold bore effects.

@Bill Alexander Thanks for the amazing post. A bit late but hope people will catch all this fascinating info. The piston/rod is very long, where in the barrel is the gas port located? 14", 15" mark?

@Vitor Roma 19" from the breach . The piston is essentially the carrier with a 22" bearing surface. What one may consider the carrier typically, is about the size of a Snickers bar and simply provides a location for the cam tracks. and the second bearing surface for the mechanism.

I wonder if people will review the information or simply dismiss it as a sales pitch.