High Velocity Powder-Actuated Tool is used for normal concrete not harder than C40. The nail initial velocity is very high as there is no piston but high pressure gas to push it.
Powder-actuated tools come in high-velocity and low-velocity types. In high-velocity tools, the propellant charge acts directly on the fastener in a process similar to a firearm. ... Powder-actuated Fasteners are made of special heat-treated steel. Common nails are not used for powder-actuated fastenings.