Mixing missile types (or turret ammo types) is a bad idea across the board, for a couple reasons.
First, convenience. If you use the same ammo in all weapons, you can hold Shift and click+drag to group those identical weapons together. That means that instead of needing to push 7 buttons for your Corax to fire its 7 launchers, you can just push one. Mixing ammo messes this up.
But more importantly: peak performance. Whether you are doing PvE or PvP, you want to be maximally efficient at dealing your damage. To illustrate the arguments I make, let’s consider a hypothetical ship that only has two missile launchers and let’s pretend that only two damage types exist: EM and Explosive. Since with two launchers you have two choices of what to load, you have three choices:
Load one with Mjolnir, and the other with Nova, covering both damage types. You might think this is the most balanced approach, but it means that against something that resists EM damage very well (such as an armor-tanked player ship, or an Angel NPC) you will be missing a big chunk of potential damage.That is, when you are fighting such a ship, your ship is not performing at its peak – which can well lead to failure or death.
Load the same type in both (for example, Nova). This means that you would be operating at peak potential against the chosen target (for Nova, armor ships), but even more poorly than if you mixed ammo against shield ships. For PvE, this is the preferred option since the resistances of each faction’s NPCs are well known.
Load one and keep spare ammo of the other type to switch to in your cargohold. It takes either 10 seconds (missiles, projectile turrets), 5 seconds (hybrid turrets), or no time at all (lasers, drones). This means that you can evaluate your situation and pick the right ammo to load uniformly in your weapons before each fight. About to fight a Drake? That’s a shield ship, load Mjolnir! Oh, it’s a Maller? Some Nova will break its armor. A Hurricane? That’s a toss-up, either use other clues (like its speed) or just pick one and pray you guess right.
Both option 2 (for PvE) and option 3 (for PvP) are superior to mixing ammo. Using knowledge and situational awareness, you can maximize your ammo’s contribution to your ship’s stats.
Some extra notes that are relevant to ammo choice:
- This advice applies to range/tracking/etc considerations as well as damage type; always use the ammo that gives you the best damage for the range/speed you are going to be fighting at.
- Sometimes it’s even worth switching ammo mid-fight if your approach isn’t working.
- Some missile ships (like the Corax or Drake) bonus one damage type over others. With good skills, this bonus is so big it’s almost not worth bothering to bring anything but the bonused ammo type. For the Corax, Drake, and a few other Caldari ships, that means kinetic (or, “Scourge”).
- Some ammo is simply not worth it in some guns. For example, blasters lose a ton of damage for only a tiny amount of extra range by using anything other than Antimatter (or Null/Void). Autocannons should never load anything other than EMP/Phased Plasma/Fusion (or Barrage/Hail) for the same reason.
- PvP damage resistances are not always obvious. A shield ship might actually be weakest to Thermal, not EM, as it might have plugged the EM weakness in expectation that people will shoot that. Additionally, T2/T3 ships have extra weird racial resistances. For example, T2 Amarr ships are weakest against Thermal/EM despite being armor ships.
That’s enough information overload, I guess. Hope it’s useful!