New Scientist has reported on a company that is developing a “Variable Velocity Weapon System” that works by

mixing a liquid or gaseous fuel with air in a combustion chamber behind the bullet. This determines the explosive capability of the propellant and consequently the velocity of the bullet as it leaves the gun. “Projectile velocity varies from non-lethal at 10 metres, to lethal at 100 metres or more, as desired,” says Lund.

The concept of a variable amount of gas is not new, pump air guns have had this feature for a long time but, at least according to the article, the gas is ignited making it a true firearm.

Interesting concept. Although I wonder about how useful it is compared to existing systems: a non lethal gun and a lethal side arm.

Another company filed a patent in 1997 for a “Variable Velocity Weapon System”. The system they describe ports gas from behind the projectile to in front of it creating pressure and slowing it down. Sounds like a great idea to create huge amounts of pressure and blowing up the barrel.

From the patent:

The present invention relates to weapon systems that accelerate projectiles using gases generated by the rapid combustion of a solid propellant, in particular, such a weapon system is able to vary the barrel exiting velocity of the projectile through a barrel venting means. In one embodiment, a front venting means exhausts gas generated by combusting propellant from behind the accelerating projectile and redirects a portion of the exhausted gas either to at least one fixed volume, to the front of the projectile, or to a combination of at least one fixed volume and to the front of the projectile. Redirecting some of the exhausted gas to the front of the projectile restrains the projectile, thereby slowing the projectile, and thus further decreasing the muzzle velocity of the projectile. In another embodiment, gas from behind the projectile is exhausted into a fixed volume, thereby decreasing projectile acceleration, and thus, the muzzle velocity of the projectile.

Cross section of the ported barrel.

Hat Tip: Slashdot