Forward Grip or Barrel Shroud
In the wake of World War II, several manufacturers introduced an interesting concept -- the machine, or assault, pistol, which fell somewhere in between semi-automatic handguns and fully automatic submachine guns. Machine pistols could shoot in full automatic or burst-fire mode, but they used smaller-caliber ammunition. Even with this concession, they were notoriously difficult to control, as the recoil caused the tip of the weapon to drift.
One way to tame machine pistols is to incorporate a forward grip. The Beretta 93R, for example, comes equipped with a small kickstand-like foregrip to help improve control when it's operated in burst-fire mode. This allows the user to counteract the effects of recoil by holding the front part of the weapon with the non-trigger hand. Another trick involves covering the barrel of the weapon with a perforated tube of metal. Known as a barrel shroud, this simple addition allows a shooter to hold the weapon more securely without burning a hand on the hot barrel.
A few semi-automatic handguns still echo the designs of their fully automatic machine-pistol cousins. The Intratec TEC-DC9, or TEC-9, stands as one of the most notorious examples. Used by the shooters in the 1999 massacre at Columbine High School, the TEC-9 received its magazine in a compartment located in front of the trigger. This provided a convenient grip for anyone hoping to exert two-handed control over the weapon. Some TEC-9 models also featured barrel shrouds and shrouded barrel extensions.
Today, forward grips and barrel shrouds remain fixtures in assault-weapon legislation, despite criticism that these are cosmetic enhancements and don't contribute to the lethality of a gun.