Pistol versions of the AR-15 are not uncommon, but the Piston Driven System (PDS) pistol from Rock River Arms offers a major difference. Due to its piston system, the PDS does not have a recoil spring tube protruding from the back of the receiver, which keeps overall length to just 17.5 inches. Another advantage of the PDS is that an owner who wants to pay the tax and register it as an SBR (Short Barreled Rifle) is ready to go after adding a shoulder stock (note that it is illegal to add a shoulder stock without registering the PDS as an SBR).
For those who want to keep the PDS a pistol, there are some advantages as well. Although 17.5 inches overall and 5 pounds in weight is still big for a pistol, the PDS is still relatively handy, and it does give its user a rifle-caliber weapon. For example, in Missouri where I live, anyone 21 years of age or older who may legally own a “concealable weapon” may carry it loaded in a vehicle. However, he or she may not carry a loaded rifle or shotgun without having a concealed weapons license. The PDS Pistol would seem to give another option as a legal car gun. Of course laws will vary from state to state, and should be checked before carrying any weapon.
For anyone familiar with the AR-15 or M16, the controls on the PDS are quite similar. The safety is the same lever, easily operable by the right thumb when in shooting position and the magazine release is in the same location. Also the same is the bolt release lever located on the left side and easily hit by the palm of the left hand when shooting right-handed. However, one aspect of operation is completely different. To operate the charging handle, one does not grasp the commonly encountered handle at the rear of the receiver.
Instead, a folding ambidextrous, non-reciprocating handle is located at the front of the upper receiver. For those familiar with the charging handle on an FN FAL Para model, this one is quite similar. I actually like the location as it easier to operate while holding the pistol in one hand and does not require the added space needed to pull back a standard AR charging handle. The Hogue rubber pistol grip is also of standard AR type pistol grips.
An “Operator Safety Flange” is incorporated into the injection-molded handguard. This flange serves to prevent the support hand from slipping forward in front of the muzzle, a useful feature on any short-barreled PDW (Personal Defense Weapon) type firearm.
The upper receiver has an extended Mil-Std-1913 rail. Another short Mil-Std-1913 rail is located on the bottom of the regulator housing for the attachment of a sling swivel or light. Note that attachment of a vertical foregrip at this position might appear desirable and probably would be, but to do that it will be necessary to register the PDS as an AOW (Any Other Weapon) with the BATF and pay the tax. There is also a vertical Mil-Std-1913 rail at the back of the receiver which can be used to attach a sling.
The 8-inch chrome moly barrel has a 1-in-9-inch twist, which allows a wide variety of 5.56mm rounds to be used. A PDS-MD 1/2-28 thread muzzle device is supplied on the PDS Pistol, and this standard thread allows installation of a variety of flash suppressors.