Glocks are some of the most efficient and versatile handguns of all time. Now they don't make a rifle (yet) but a number of companies do offer conversion kits to allow you to convert your Glock handgun into a pistol caliber carbine. One of the most popular ones is the CCU made by Mech-Tech.
Why a carbine kit?
Springfield Model 1855 Pistol Carbine, About 4,000 were manufactured in 1855 and 1856, an saw limited service usage with the US Army Cavalry.
Pistol caliber carbines date back to the 1850s and the concept in and among themselves are not new. Taking a standard handgun action and adding a short, rifle length (16-20 inch) barrel and a buttstock, you now have a longarm that still fires a pistol round. The stock and forearm provide a much better and more stable platform than a pistol's grip alone. With a longer barrel, you get a longer and much more accurate sight radius. This means that basketball sized groups at 25-yards with a handgun can very easily become softball sized groups with that same handgun in a carbine configuration. With a little practice and a steady shooting position, 100-yard shots are a real possibility. You just can't do that with a standard handgun.
The Mech-Tech CCU
Mech Tech of Kalispell, MT, offers what they bill as their Carbine Conversion Unit (CCU) for Glock-series handguns. The CCU is officially a handgun accessory according to the ATF and only your Glock itself is the controlled item. They are offered for G17; G17C; G34; G19; G19C; G20; G20C; G21; G21C; G22; G35; G22C; G23; G23C; G31; G32; G32C and the respective 'SF' models. For those sharp Glockheads out there you will realize that this is almost every model but the full-auto G18/18C, and the 10mm and 45 ACP compact series pistols.
The CCU installs simply, using your Glock's grip-trigger-rail assembly as the lower and Mech Tech's accessory as the loaded upper. The installation itself is reversible, and leaves no damage.
The basic CCU includes a 16+" barrel, internal slide, recoil spring, cocking handle and exterior rails. It retails for about $350. If you add their optional MonoRail, MiniRail and M4 stock with adapter to your basic CCU, you have a shootable carbine kit for about $530.
This price point makes it tempting for a the average buyer to instead purchase a separate and stand-alone Kel-Tec SUB2000 carbine that, while is not a Glock, will use your same Glock-series magazines. However, if you just need a Glock carbine...the Mech Tech CCU could be for you.