Is there a point in designing general AMMs with more than 1m km of fuel? It seems pretty pointless as the practical range is limited by the size/cost of the active sensors and fire controls needed for it, at the fuel points given on the wiki one would need a max-size tier 4 active sensor to use the "short range" AMMs at anywhere close to their max range.
Sometimes its helpful to be able to fire multiple volleys against a missile, just in case your AMMs aren't very effective. Say an enemy missile goes 50000 km/s (which is actually quite possible for precursors to have, in my current game they're 55 and 56 thousand km/s) at that speed it's moving a quarter million km every 5 seconds. Say ten enemy FACs fire a volley of 90 at you, your missiles need 3 to destroy each since they're so fast, and you only have 40 launchers. At 1m km your fire controls fire 40. At 750k km another 40. At 500k km another 40. At 250k km your missiles will have probably hit and destroyed 40 of them, and your launchers probably fire more, but the 50 enemy missiles will probably hit you in the next 5 sec increment before they intercept them.
If you had 2m or 3m km range missiles and sensors you could have had time to shoot at all of them. It's true that early on getting the sensors powerful enough to go out that far can be problematic though. The other useful thing about longer range anti-missiles than 1m km is you can use them as a last resort to pelt enemies before they enter beam range. Sometimes you might face a foe that your regular missiles can hardly hit (say an enemy FAC going 12,500 km/s), so missiles designed to intercept other missiles can be helpful against them.
And I believe you get a bonus to hit missiles the longer you've been tracking them, so the farther the better.
He asked about range on anti-missiles, not range on sensors
I think that bonus only applies to beam PD too doesn't it? I've never really noticed if my anti-missiles were getting a tracking time bonus or not.
And longer range sensors basically let you ignore ECM vsince all it does is reduce your sensor range against them.
ECM doesn't affect sensors. ECM reduces the range of your missile fire controls, and reduces the hit rate of beam fire controls. Large missile fire controls can ignore the ECM penalty though. For beam fire controls you can never just ignore the ECM, as its a percent off your hit rate and the hit rate goes from 100 to 0 (point blank and max range). A 50% ECM would act like you were at max range even at the 50% range, and act like the 50% range at point blank. In their case it's usually more effective to slap on an ECCM than try to further increase range, because no matter how much further ranged your fire controls are they still have a max accuracy of (100 - ECM rating)% at point blank. If I'm going with nothing but missile ships I never even bother researching ECCM, but with beam ships it can make a big difference.
Speaking of scientists, I have crazy good ones in my current LP. 65% bonus 45 labs energy weapons, 60% bonus 50 labs sensors, 60% bonus 60 labs power and propulsion, 45% bonus 30 labs construction and production, 20% bonus 30 labs defensive systems, 15% bonus 45 labs logistics. Only thing I'm lacking (and have never filled in even after getting 12 new scientists) is a missile/kinetic weapon guy. My EW guy is currently researching missile tech, heh.