In three runs through the canyon the MK112 performed incredibly well. Wind was whipping up, making it very difficult for my pilot to stay steady, or get as close as was desired. Targets in the 50- to 75-yard range were struck with regularity, longer ranges not so much. A red-dot remains the best option here for sure. By the third run misses were less frequent. Either way, what a blast! Even with the brass catcher, the MK112 worked great, and the Gemtech suppressor was fantastic. Almost no recoil and no muzzle blast made it easy to stay on target, even in the shifting wind and an occasional abrupt change of position in the helo.

Final Thoughts

This was the third configuration with this rifle. Initially it was tested with no suppressor. It ran reliably with all the 110- to 125-gr. ammunition wide open using a standard carbine buffer and spring. Moving to the 147- and 149-gr. ammunition it was more finicky. PNW 147-gr. ran without a hitch, as did some of my hand loads. Neither the Gemtech nor the International Cartridge ammo would lock the bolt open on the last round consistently. Adding various suppressors, the 187-grain Gemtech, 220-gr. Remington and 208-gr. Hornady AMAX subsonics ran fine. With the GMT-300 suppressor attached, it was the most reliable over the broadest range of ammunition.

The author was able to wring out sub-MOA precision at 100 yards with the short-barreled PWS using Remington 125-gr.OTM ammunition.
The author was able to wring out sub-MOA precision at 100 yards with the short-barreled PWS using Remington 125-gr.OTM ammunition.

Overall the MK112 was very soft to shoot, accurate and reliable. Add the suppressor and it gets a bit long, but if you want to run without a can, and over a very broad range of ammunition, this 12.75” piston gun is an excellent choice.

As expected, velocity loss was minimal compared to a 16-inch barreled 300 BLK, yet much better than the shorter barrels. Barnes new 120 grain TSX made 2,100 f.p.s., and the 125-grain OTM made 2,250 f.p.s.—both only 90 f.p.s. slower than previous tests in 16-inch barrels.

Primary Weapons rifles lend themselves well to suppression. They run cooler, although there is a bit more gas in the action. This setup was about perfect. It stayed clean, ran cool and there was very little excess gas during hard use. If you want something just a bit longer then a pistol length barrel, the MK112 may be exactly what you need. For more information contact Primary Weapons Systems, Dept. OT; Tel.: (208) 344-5217; Web:

Load                                                                          Velocity                      Accuracy

Remington 125-gr. OTM                                             2,250                           0.80”

PNW 147-gr. Practice                                                 1,900                           1.60”

PNW 125-gr. Match                                                    2,250                           1.00”

Barnes Vortex 120-gr. TAC-XP                                    2,100                           1.25”

Barnes Vortex 110-gr. TAX-XP                                    2,320                           1.30”

Hornady 110-gr. VMAX                                               2,400                           1.40”

Gemtech 149-gr. FMJ                                                1,830                           1.55”

International Cartridge 149-gr. frangible                     1,790                           1.58”

Tested for velocity using Pro Chrony Digital chronograph. Accuracy in inches for 5-shot groups at 100 yards from a prone bag rest.