If you're a rebel, one of your special skills at the 4th tactics box is "underway replenishment". This skill reloads your missile launchers in space and costs about 3K credits usually regardless of how many launchers you are reloading.
Here's the bug: Lets say you buy Proton missiles, which normally have a 0.5 Vs. Armor and Shields multiplier on them (multiplies the min-max damage, but since it's 0.5, it's actually less damage), if you use underway replenishment, you will get missiles with 8.0 MULTIPLIERS! That's right, 8 times your min-max damage.
The way underway replenishment works is like this. First, you'll have to be 4th tier anyway to use this skill, so go get yourself either a MK III or MK IV concussion OR proton launcher (I use concussion MK III because I fly an A-Wing and that launcher is usually around 5K mass, vs the Proton launchers are about 14K mass). Ok, you have your launcher(s), now, buy a missile pack from a vendor for each of the launchers you'll be using (in my case, concussion MK III pack, which is about 8K max damage).
NOW, load your launcher into your ship, load the ammunition too, and head up into space, waste some of your missiles (because underway replenishment won't work with a full launcher). Now, call for underway replenishment, you actually want to hit the button twice because the first time you hit it, it just brings out the refill ship, the second time you hit it it actually confirms you want to pay the 3K to refill. Your engines/reactor will cut out temporarily during the replenish, don't worry they will turn back on as soon as you're reloaded.
Now, hit V or whatever your key is to see your ship systems chart, and check out your ordinance. The missiles now in your launcher should be 8.0 multipliers Vs. Armor and Vs. Shields, and the min-max damage is probably about 500 lower than the original pack you loaded. Every time that you do underway replenish it gives you missiles of a little lower damage, but the multipliers are always 8.0, which is a hell of a lot more damage than 0.5.
I tried using two mark IV Proton launchers with 8K max replenished missiles and 8.0 multipliers, and I took out a decimator in 1 launch. Load up a MK III concussion launcher with an 8K pack and replenish it and you'll be able to 1-shot tier 5's all day.
The key is to always have a few bought missile packs with you because eventually after about 10 or so replenishes, you'll be getting down to about 1K max damage, but you'll still have that 8.0 multiplier. When the damage starts gettin low, just load another bought pack and you're good for another 10 or so replenishes till the damage gets low again!
And this works with ALL MISSILES! I tried it with MK II Spacebombs and I replenished 20K max damage 8.0 multipliers! :O Fire that at a gunboat!
Ya can't beat that for 3K credits a replenish. This skill will also reload your countermeasures automatically, if you have them installed and a pack was already in there.