A new company called Holland Automatic Rifles (HAR) are developing a new AR-15-style upper receiver and piston system.

John from HAR explained how their system works …

It works on a new principal, of venting most of the unused gasses before they enter the piston. Then actuates the piston, before venting at the mid cycle, then vents a third time as it returns to rest. All of the exhaust gasses are vectored, so as to reduce muzzle climb, and torque twist. This principal has proven to need little or no lubrication, and acts as a cooling aid as well.

I am sure John will answer any questions you may have.