A low-speed projectile is designed for forming relatively large apertures in walls against which the projectile is fired. The projectile includes a penetrator core having a cavity containing an explosive charge activated by a time delay fuse circuit. The time delay is chosen to cause explosive ignition when the cavity and explosive is within the wall to be pierced. The construction of the projectile directs the explosive impulse radially, creating a hole in the wall considerably larger than the outside diameter of the penetrator's core. A preferred application is a projectile for a shoulder-fired weapon.