If you have little to no gunpowder at all in your shell, your gun won't need cooler pieces; it won't need to cool down between shots at all. Thus, with enough stored energy in the magnets (the bits next to the firing piece), depending on the energy used per shot you can fire every single shell you have loaded all at once.
For example, if you have 2 magnets for 10,000 energy stored, and use 1000 energy per shot, you can fire 10 shells all in the span of like, half a second.
1717 This is super useful for both getting through an enemy's LAMS defense, and for boring holes into enemy armor relatively quickly.
Another thing you can do with railguns is, like mentioned, using 0 gunpowder in a shell. This means that combined with a shell that is pure kinetic, your gun has absolutely 0 chance of exploding if any of the loaders or clips get destroyed, without needing ammo ejectors.
You can combine all of this for really effective CIWS throwing pure kinetic heavy head shells at small diameters very quickly, most useful for anti-missile or CRAM defense. Swap the heavy head out for AP or sabot for "sandblaster" rounds more suitable for stripping armor due to their high AP