by Paul Markel

All machines, if they are around long enough, undergo some kind of evolution. Today's Ford Mustang is not the same car it was decades ago. So it goes with the AR-style rifle. The AR15 that Gene Stoner introduced in the 1960's has undergone a serious evolution. I believe most shooters would agree that the current crop of 'black rifles' is more reliable and robust than that which were shipped to Southeast Asia all those years ago.

Naturally, all these changes did not occur overnight. Enterprising engineers and gunsmiths have considered the AR and offered improvements in the controls, the internal components, and the outward appearance. Of course, not every 'improvement' or modification has stuck, and various manufacturers have components that are unique to their own brand.

One of the chief complaints of the M16 or AR series from the beginning was the operating system, specifically how the gas was used to cycle the weapon. When the rifle is clean and properly lubricated, most all AR's will run superbly and shoot tight groups into their targets. However, carbon build-up and fouling from burnt propellant can gum up the works and retard the action.

Some gun makers have faulted the shooter for using 'dirty ammo' and suggested that only certain brands be fired from their rifles. Others state that the rifle must be stripped and cleaned after 'X'  number of rounds have been fired through it. While every machine runs better when cleaned and properly maintained, field conditions and heavy use may preclude regular takedown and clean-up.

Consider the current conflicts in Iraq and Afghanistan. Our soldiers and Marines have been engaged in protracted urban battles where men have fired hundreds, if not thousands of rounds from their individual weapons. These engagements have gone on for extended periods and taking apart the rifle for a scrub-down was not a practical matter.

KKF M9Evo

The gas piston system is not a new idea; firearms engineers have been working on it for some time now. Keeping the gas out of the action and away from the bolt carrier group is the reasoning behind the gas piston. The trick for designers has been to come up with a gas piston operating system that's robust and reliable.

Kurt Wala is a gun builder and engineer from Bushnell, Florida and he has been working with the black rifle for some time now. Several years ago, Kurt set out to design his own version of a gas piston operating system and the results of his efforts is what he now calls the "M9Evo".

 The basic concept behind Kurt's design was to modify the operating system so as to virtually eliminate all gas fouling from the chamber and the action by using a piston driven pushrod. Step number one on the to-do list was to design a stainless steel piston. The piston would harness the propellant gases out front, ahead of the bolt carrier. With the piston complete, Kurt had to modify the gas block next.

Kurt Wala fabricated a new (1) gas block to accept the (2) piston as well as the (3) front sight and (4) bayonet lug.

The standard 'A-frame' style gas block/front sight base is made for a slender gas tube, not a piston. Mr. Wala fabricated a brand new gas block from steel billet that would mate up with the piston. The block would have a Picatinny-style rail to accept a fold-down/flip-up front sight and included a standard configuration bayonet lug.

Next on the list was the operation rod (op rod) assembly. The piston itself does not move; it guides the gas into a stainless steel piston cup. A quarter-inch titanium intermediate op rod mates up with the cup.  To the rear, a stainless steel pushrod mates with the titanium oprod. The pushrod is the piece that actually makes contact with the bolt carrier. This rod has a return spring and is supported by a stainless steel bushing to guide it over the barrel nut and into the upper receiver.

The (1) pushrod, (2) guide spring, the (3) oprod, and (4) piston cup are disassembled.

The last major component in the conversion would be the bolt carrier. Specifically, the standard AR gas key would be removed and a solid carrier key would replace it. The new carrier key has a cup to mate with the stainless steel pushrod. If you are like me, you need to actually see and touch the parts to get a solid understanding of the operation. Even though the whole process was explained to me by Kurt via e-mail, I did not grasp the simplicity of the design until I had the chance to take it all  apart and examine it.

The redesigned bolt carrier key mates up with the pushrod.

With the gas piston system, only the upper receiver is modified, the lower receiver and action are standard AR design. The M9Evo upper can be mated with most AR lowers (re: any, per Kurt). I was shipped the complete upper receiver. I had a number of AR-style rifles on hand, but I felt that the Rock River LAR-15 lower with a retractable stock would be a good fit for this project.

Range Time

My primary intention would natually be to test for reliability and function. For a fighting carbine such as this, tight little groups are a secondary consideration after dependability. Kurt reported that he has put some 500 rounds through the upper receiver before sending it to me for review. When the gas piston gun arrived, I had an ammo can full of various 223 loads set aside for the test. First things first, I had to check the sights and do some chronographing. A couple of clicks to the rear sight and I was in the 10 ring at 75 yards. Test ammunition would come from Black Hills, CorBon, Federal, International Cartridge Corp., Winchester, and Wolf.

For my slow-fire testing, I would shoot from a sandbag rest at 75 yards. Velocity and accuracy results were what you would expect from a carbine. Rather than just burn up ammo trying to make the gun quit, I used the opportunity to train and run though a number of drills. I engaged both paper and reactive steel targets. My paper targets included the "Crazy Bones" series from Thompson Targets of Canton, Ohio.

The steel target came from a company called Safe Directions, LLC. The Urban Rifle Target is constructed of half-inch AR500 steel. In addition to the steel target, the unit includes a stand consisting of two legs and a cross bar. The entire target weighs 48 pounds, but a single person can assemble it in minutes.

In addition to normal shooting exercises, I wanted to improve or at least reinforce my skills with a carbine. For this review I had looked once again to the Brownells catalog. I picked up some new 20-round magazines, Friction Defense gun lube and a PACT Club Timer III. The PACT timer and magazines are listed in Brownells new products flyer.

While many people will associate digital shot timers with handgun training, they have an application with rifles/carbines as well. Taking a tip from my friend Walt Rauch, I worked on the One Shot Qualification. For this drill I would begin with a loaded magazine in my off hand and the unloaded carbine in my right. The bolt was down on an empty chamber. My goal was to insert a magazine, load a round, disengage the safety and put a single round into a silhouette-sized target from 20 yards all in under 4 seconds. My first attempt was around 4.5 seconds. Several shots later I seemed to be stuck at 4.11 seconds. Finally, I hit 3.89 seconds and was satisfied.

For the next timed drill, I would start with the carbine loaded, safty on, standing at low-ready position, Goal: Three rounds into silhoutte at 5 yards under 1 second. On the first 'beep' I managed 1.01 seconds. I hovered around a second in the 0,95 area for a while. My best time was 0.89. Lastly, I decided to try one shot at 5 yards, standing low-ready with a 0.5 second goal. This proved to be the most challenging of all. After about a dozen rounds, all in the 0.6 to 0.7 second range I managed 0.55 seconds. What is the point in all this? First I was able to set goals and gauge my progress. If you wish to improve at any endeavor, you need a way to gauge or measure your progress or lack thereof. Secondly, I challenged myself. Again, if you want to improve your skills, you need to challenge yourself. If not, you will soon find that you are stagnating and worse, that your skills are waning.

Extras

My gun reviews invariably give me the opportunity to work with new gear and accessories and this time was no different. BlackHawk has just released a new Magazine Coupler for the AR. The coupler holds two 30-round magazines together for a fast mag change. What makes the coupler unique is that it has a fixed standoff point and comes with a tethered 'top round protector'.

Guns and ammunition are important, but you don't go into the field or range without your clothes. Tru Spec now is one of the leading manufacturers of military and field clothing. Their newest camoflage pattern is called 'Multi-Cam'. The material blends varied shades of green and brown. This makes the pattern more viable for  summer, spring, and fall. I have been using Tru Spec uniforms for a couple of years now an always found it to be top quality.

Final Notes

Several hundred rounds into the test, I decided to take the gun down for a quick cleaning and inspection. I was pleased to find out that only a minimum amount of carbon was found on the bolt/bolt carrier. You are always going to get some carbon on the bolt.

The majority of carbon buildup was right where I would have expected it, on the gas piston and piston cup. Disassembling the oprod assembly was simply a matter of compressing the pushrod and slipping out the titanium oprod. The other pieces all slide right out.

I gave all the components a good once over and then applied a coating of Brownells Friction Defense lube to all the moving parts. This would keep the gun running smoothly for several hundred more rounds.

Before I set down to pen this piece, I loaded up a 20-round mag full of Black Hills new 'Varmint Grade' ammunition. Using a Barnes bullet, this lightweight .223 projectile comes apart violently on impact. I headed out to the field and whacked a couple of good sized groundhogs with the carbine/ammo combination. You know what they say, "All work and no play makes Paul a dull boy."

If you are a sport or competition shooter and your primary aim is to shoot one round at a time from your AR, the new gas piston system may not be all that interesting to you. However, if you burn a lot of ammunition either in training, or in the field, a more reliable, cleaner carbine should be on your list.

At the moment the M9Evo operating system is in its infancy. How will it fair in the future? Only time will tell. I can merely report that the example I had to work with operated without flaw and that is a pretty good way to start.