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Preview – POF Piston Driven AR

Photography by Henry Z. De Kuyper

Patriotic Engineering
Piston Driven. 308. AR. Machine Gun. Any Questions?

It seems like everyone and their brother is making a piston AR these days, but it wasn’t always so. Patriot Ordnance Factory was one of the first companies to bring to market a system that combined some of the best qualities of Stoner’s design along with bits borrowed from elsewhere and has held a patent for a piston bolt carrier since 1992.

We got the inside scoop on their operation from company founder and president Frank DeSomma, then took one of their 12.5-inch barreled full-auto carbines to the range to see what kind of performance it turned in. And in what’s fast becoming a RECOIL tradition, we managed to bugger it up.

Preview   POF Piston Driven AR photoPreview   POF Piston Driven AR photo

Let’s face it, these are not cheap guns. But a Porsche isn’t a cheap car, either, and — celebrity endorsements and slick marketing aside — price is usually an indicator of quality. We got to look behind the scenes of the manufacturing process and came away with an understanding of the engineering that goes into a POF rifle, and why they’re among the most accurate piston guns available.

Aircraft Accurate
Accuracy is all about eliminating variables. While mere humans will probably never get to the point where we can send identical bullets downrange at identical velocities and under identical conditions, the closer we can get to that ideal, the nearer we’ll be to ballistic perfection. Ammo variables are a whole ’nuther ball of wax, but when it comes to the firearm, we need all of the important components to be concentric, square, and parallel to each other. In a bolt-action rifle there are just three major components to worry about — the receiver, the bolt, and the barrel. In a basic AR pattern rifle there are six (see if you can name them), so the potential for accuracy-robbing variables is double that of a bolt gun. Add a piston system to the mix and it’s easy to see why precision machining is so vital if we want to hold group size to a reasonable level.

POF does as many of the critical machining steps as it can in-house on modern CNC machines, cranking out bolts, carriers, barrel nuts, gas blocks, billet upper and lower receivers, as well as a bunch of small parts. Barrels arrive as 5R rifled blanks and are then profiled, chambered, and headspaced in-house. “I was in the aerospace industry before starting up POF,” DeSomma explains. “A buddy was thinking about buying a new CNC lathe and I told him if he did that, then we had figure out how to make barrels. We made a lot of mistakes, but we learned what it took to make a great barrel.” Two twist rates are produced, a 1:8 in 5.56mm and 1:10 in 7.62mm, which are then sent to a local subcontractor to be nitride finished inside and out to a surface hardness of RC70.

Preview   POF Piston Driven AR photo

Unlike the barrel extension in a typical AR, the POF version is precision ground, rather than turned. This is a much more expensive process, but it allows tolerances on that critical part to be reduced by 300 percent, again adding to accuracy. Another practice carried over from aircraft manufacturing is the traceability of key parts. In the event of a plane augering in, the FAA investigates exactly why it hit the deck; if the cause winds up being a dodgy widget, they want to know how many others like it are out there and pull them from service. POF does much the same, numbering barrels, gas blocks, and carriers, as well as date-stamping small parts such as extractors.

For the rest of this article, subscribe digitally here: RECOIL Issue 7