[yhwhsman]

far superior alternative from the Phalanx guns

I don't. When a Phalanx runs out of ammo, you slap in (relatively speaking) another magazine. If Metalstorm runs out of ammo, you have to replace an entire barrel.

[supercat]

If Metalstorm runs out of ammo, you have to replace an entire barrel.

How far from the front of the barrel is the foremost projectile before the weapon is fired for the first time? Might it be possible to design the weapon to breach-load cases each of which had a bunch of projectiles within it?