We at Umbrella Armory have followed Retro Arms since their inception. Many of their products are good, but when it came to pistons it was often a hit or miss. We've followed them when their first pistons came out and there were always some issues with them. Staying cautious we watched and always revisited each product when a new generation was released. However even then, with their CNC POM variants, we weren't impressed with their performance or strength.
Until these came out.....
Retro Arms did finally make a piston we were proud to carry. We're picky with our pistons, we demand simply too much from them such as...
-Strength to survive PME
-Long term wear resistance on release tooth
-Piston Body fitment
-Piston Body wear resistance on rails
After being strapped into a couple tester monster builds ranging from 570FPS DMRs, to 50+RPS 400fps DSG powerhouses. We've concluded that these pistons are worth every penny. They resolve a lot of issues with normal pistons while keeping the price surprisingly low.
The Piston Body: Due to their design of a closed hole, the rack is superiorly supported, quite the best of its kind. The steel rack, no longer can be pressed into the middle, and has tons of surface area for glue reinforcement (which though we haven't disproved it being needed, we still recommend as a good thing to do regardless). The rear tab is reinforced and quite often the point of failure during PME, or jamming situations. This piston has the highest chance of survival against the heaviest of abuses. Full rails allow for even wear distribution on both the piston, and gearbox rails. We have noticed over 2-3 years or over 100,000 rounds wear is noticeable along both the gearbox's piston rails, and piston itself. Sometimes enough to cause failure, due to the added meat these piston gives we don't see this happening until 2x-3x the length of time.
Steel Teeth: Machined exceptional well with great tolerances piece to piece. Its certain to say that pistons are coming out with better and tighter QC then initial generations. We've tested the racks to be a uniform 50HRC+, while scratching at 55HRC, giving exceptional wear resistance and higher than many competitors. They also are press-fitted into the body, and is more difficult to remove than any other piston we've worked with. We applaud Retro Arms for keeping their tolerances tight.
Weight: 16.91g Length: 66.56mm Width (excluding rails): 18.55mm Total Width (including rails): 22mm Height (including main teeth): 20.84mm Height (just body): 19.3mm Height (pickup tooth & body -- the tallest area of the piston): 21.12mm
Note: Not compatible with springs ABOVE an SP170. MS180s/190s or MS210 wouldn't fit inside the piston body.