March 2011

Split the Difference: Is a $700 5.7x28 Upper a Good AR Buy?

Getting more performance out of your existing AR-15 can be done by adding an aftermarket upper. But is 57Center’s PDX unit chambered for a bottlenecked rocket the right choice?

The evolution of the AR-15 continues apace, with a host of manufacturers building out the 223 Rem/5.56mm modular-rifle concept to a bevy of cartridges that offer more power (6.8 SPC, 30 Carbine) or cheaper operation (22 LR, 9mm). These chamberings appear in dozens of rifles and dozens of replacement uppers. The uppers usually cost slightly more than half the price of a complete gun, and they snap onto AR lowers, which gives owners a choice of cartridges to shoot on a given day.

We recently pitted once such device, the 57Center’s piston-driven AR57 PDW Upper in 5.7X28mm, to three previously tested guns that were highly rated, the direct-impingement Stag Arms Model 2T 223 Rem/5.56x45mm NATO, $1125, Smith & Wesson’s M&P 15-22 No. 811030 22 LR, $569, and the Olympic Arms K9 9mm, $834. The AR57 PDW Upper came to us via Collectors Firearms in Houston (, which listed the used 5.7X28mm upper for $550. New AR57 PDW Upper units are available from the company or from Brownells for $696. The PDW upper was attached to a CMMG Model 4SA lower, which lists for $296 from CMMG (

On a whole-gun-to-gun basis, a new 57Center AR57A1 PDW Carbine costs $1099. The whole carbine weighs 7.45 pounds and is 33 inches long with a 16.04-inch standard barrel. It includes an AR57 Flash suppressor with standard 1/2X28mm threads), a custom pistol grip with battery and accessory compartment, M4 Carbine 6-position stock, and four AR57 50-round magazines. Down the road, it will certainly be interesting to compare a selection of uppers against each other, and we’ll continue to pit guns in alternate AR chamberings, but for now, we want to gauge whether we’d plunk down $600 to $700 after taxes for the AR57 PDW Upper. In our opinion, we believe there are significant reasons not to.

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