If the accelerator can get the projectile above .866c without using too much antimatter to do so, I guess.
Incidentally, it's worth noting how chemical bonds behave at high velocity: Above 10km/s, solid matter behaves as a liquid, for purposes of impact physics. Above 100km/s, matter behaves as a gas, for purposes of impact physics. At high relativistic speeds, matter basically behaves like the compressed globs of energy it is, and will go all over the place with considerable eagerness.
It is worth noting that while overpenetration is a thing, it's less of an issue when your projectile hits hard enough to force nuclear reactions in the target. At those energies, even if the expanding cloud of very, very hot subatomic ash that was originally your impactor and everything in its path does make its way out the other side of the target, the radiation and secondary blast effects will cause widespread damage to any vessel of reasonable size and internal structural characteristics.
Additionally, dumbfire kinetics can be considered largely useless against spacecraft at long range (>1 light second), unless the impactor is moving at very nearly c, and even then guidance is advisable. Most kinetic weapons should be missiles with the armor protecting them against enemy point defense constituting their "warhead", potentially given an initial burst of acceleration using a coilgun or something.
(Yes, guidance electronics can survive coilgun launch, they're developing them today, let alone in the far future.)