To allow increased impact velocity, a stronger penetrator material was required. The chosen new penetrator material was tungsten carbide (WC), due to its greater hardness and its ability to withstand the greater shock and pressure generated during a higher velocity impact. As the density of WC (≈15.7 g/cm³) is twice that of steel (≈7.86 g/cm³), such a shot was too heavy at full bore to be accelerated to a sufficient muzzle velocity. To overcome this, a lightweight full diameter carrier shell was developed to sheathe the inner high density core. The name given to this projectile type was the Armour-Piercing Composite Rigid (APCR). The APCR projectile was about half the weight of a standard AP shot, but of the same diameter. Due to the large surface area for the gases to impinge upon the lightweight APCR projectile, it experienced a higher average acceleration in the gun barrel, in turn imparting a higher muzzle velocity. Unfortunately the low sectional density of the APCR resulted in poor carrying power (high aerodynamic drag), losing velocity and penetration rapidly over distance.