Let's see.

One 20-kg kinetic artillery round (mass 20 kg, obviously)

One Everest-class Dreadnought main armament: accelerates the artillery round to 0.013c.

Using the rough estimate of c = 3 * 10^8 m/s (so muzzle velocity is 3.9 * 10^6 m/s), ignoring relativistic effects, and assuming no outside forces act on the shell during its flight to target, that means its momentum is 7.8 * 10^7 kg-m/s and its kinetic energy is about 1.5 * 10^14 J.

Which means that Sir Isaac Newton is the deadliest son of a bitch in space.