Frank Stratton at our sister site All Outdoors has reviewed the Ruger PC9, the Ruger 10/22-esqe 9mm carbine. Frank writes …

The roots of its design are from the 20th Century 2nd generation carbines. That means no rails or pistol grip, no muzzle brake/flash hider, and night sights. It is a solid firearm that will take a lot of abuse and function accurately and reliably. The only change I would recommend is the addition of an electronic sight, such as the Lucid M7 shown above or an Aimpoint. While the top of the receiver is milled for Ruger scope rings, you can mount a Picatinny rail adapter to the receiver. For best cheek weld, you will want to choose a sight that is lower than those sold for AR straight stock style rifles.

Unfortunately Ruger stopped manufacturing the Police Carbines in 2006. I would love them to bring it back but sadly the market has largely gone off the concept of light compact pistol-caliber carbines. The last holdout are the classic .357 Magnum lever actions.