Intratec KG9 Registered Receiver with Factory Foregrip
The KG-9 and KG-99 have an open-end upper receiver tube where the bolt, recoil springs, and buffer plate are held in place by the plastic/polymer lower receiver frame. This design only allows for 115 grain 9mm ammunition, and if a heavier grain ammunition or hot loads are used, the plastic lower receiver will fail or crack, rendering the firearm unusable. Later versions of the TEC-9 and AB-10 had a threaded upper receiver tube at the rear and a screw-on end cap to contain the bolt, recoil spring, and buffer plate even if removed from the lower receiver, solving the problem of lower receiver failure when using hot ammo.