I've used size 50s in PDCs and also in my first ship design-- a 39kt beast.

That's changed now though-- my current destroyers are about 1/5th the cost, although they feel very light in the weapons department-- that's primarily due to the low tech level though, I managed to squeeze it all in under 9kt. Primarily from removing 50HS sensors and making a specialized design, instead of a generalized one. 5 of these ships could easily take my 39kt previous design. Ah, the things we learn.

I've toyed with the idea of sticking them in my command ships and carriers though, Good intel > No intel-- and if it comes to that I'll probably slap a few in my jumpships to pad them out if need be.

Hrm, perhaps it's gauss cannons.  I certainly remember my laser-dual role frigates costing nearly twice of my missile ships. 

EDIT:
I don't actually see the point of many small salvoes.  In my experience, it's not usually targeting that gets missiles through, although perhaps it would help against beam pd (I've only ever had to deal with minute numbers of leakers).  The large armoured missiles would usually cost alot and have low damage or performance, I find armour costing 1 MSP for 1 armour to not really be worth it.  1 MSP more engine would be far better in reducing the number of interception chances and hit rate. 

The only one I have got to work is tiny fast MIRVs.  The interesting thing about deciding where to separate your bus is that you can design a longer range AMM and see what kind of range it has and set your separation around there (AMMs need time to travel too so you can get away with some error).  ASM range quickly outpaces AMM since they can trade agility for fuel and there's no real guesswork to do. 
Eg. at fuel efficiency 0.6 and magnetoplasma, you can get away with a separation at 10mkm.  Fuel efficiency 0.4 and inertial confinement, you might need 15-20mkm. 

Actually no.  Beam ships break the bank. 
Missile ships (just the ships mind you) are dirt cheap.  It's the missiles that's expensive. 

I find on the whole that a fully loaded missile ship costs about the same as an equivalent beamship.  And it can kill the beamship easily. 

As for armoured or not missiles, you can do some simple math.  When your AMMs hit, you can tell how many missiles it takes to down one ASM.  More than 1 = armoured.  More than 3 = don't bother, it doesn't have a warhead. 

Besides, if you're willing to accept weasel missiles, the size 1 cluster missiles are far more effective as they retain a threat and are stupidly costly to shoot down.  (a size 4 bus carries 3 size 1 missiles, each taking 3-5 AMMs to get a good chance to destroy them.  5 AMMs cost about the same as the bus, the cluster missiles take a total of 9-15 AMMs to stop, easily making twice to three times cost... all while still dealing damage)

I regard the existence of weasel missiles as a sort of "bug" in the UI.  In particular, we can't set AMM launch rates against specific missile classes.  A missile with armour and no warhead would have me just ignore it after the first few AMMs hit and I find out it's heavily armoured (can calculate from chance to kill). 

In the same way that I designed but never used a "penetration-aid" cluster missile.  Essentially, instead of my normal two-stage design of a size 4 bus holding a size 3 high speed ASM, I pack in 3 size 1 missiles with 1 warhead each.  So while the pen-aid sandpapers badly, they're also essentially impossible to stop... whether by AMMs or beam pd.  (did the math on that one too, it's even more effective than armour)

What I meant to say is that missiles can be pretty useless unless you actually can bring enough of them to break the opponent and if the opponent is fast and have good beam weapons you are in serious trouble.

Not necessarily.  I find final fire beam pd to be... well, let's just say there's a reason why I dual-role my laser frigates and accept the 8x sized firecontrols.  Namely that massed missile fire from reduced launchers makes beam pd pointless.  A laser turret has ~20-30% chance of downing an equiv-tech missile (even less if the missiles are the short-range high-speed pd-penetration missile I put at the front of a two-stage design) and takes up three times the space in reduced sized launchers. 


Still, I have to try your tactics some time.  =D  Perhaps when 6.3 comes out, I'll restart with a multi-nation game. 

The problem I find with size 6 missiles is that... well, they don't fare well vs AMM pd.  And by "not well", I mean, nothing at all.  A standard 5-interception-range  AMM umbrella at equiv-tech (~20% hit chance), a single AMM launcher can hold off three ASM launchers (regardless of size) without leakers.  Five if you can tolerate occasional leaks.  (via shields or final fire beam-pd)

His fleet can be half your tonnage and if he has anything more than 20% tonnage in AMM launchers, you have no chance of getting a single missile through with size 6 launchers, even with reduced size launchers.  

I've ran a simulation of me against a mirror fleet at year 20 before with a 30+ ship fleet.  Even with 33% reduction launchers, a full fleet salvo (~1300 size 4 missiles) at my comparatively myopic range of 80mkm (which means more capable ASMs), doesn't manage to get more than one or two leakers through.  If the mirror fleet retreats while under fire, they get another pointblank interception and it's basically a 5% chance to get 1 missile through.  

A 1300 missile salvo gets 1 leaker through.  That's just sad.  Additionally, I run out of ASMs before the mirror fleet runs out of AMMs (although they're down 5% or so), downing maybe one ship.  That prompted me to redesign my missiles to a two-stage missile with a short-range "head" that has very nice stats.  On paper.  But that only brought up the leak rate to about 10-15 per wave.  

I think that your overall strategy seems sound if not overly resource dependent. I rely much less on both ASM and AMM than you do. AMM is only a tool for me to thin out incoming salvoes, beam PD and shields do most of the actual defence on my main capital ships (resource efficient in the long run) and is very large and will take hundreds if not several hundreds missiles to even put a dent in it.
One thing you can take a huge advantage of (which I don't particularly like to do) is that ships that are hit get increase in crew grade. So having your big ships hit is not actually a bad thing, it can even be the opposite.  

In general my task forces/groups can handle a mirror fleet of at least three times its own size, that is my preference and it seems you have a similar approach. Although this discussion is now less on sensors then the efficiency of missiles.

ASM can generally draw out allot of AMM by armouring them. A size 6 weasel missile (as I like to call them) can severely deplete an enemy AMM storage. If you take a mirror fleet and arm the first salvoes with 75% armoured missiles, the second with 50% fourth with 25% and then regular missiles and those AMM storages will depleted faster than ASM storages.

Then you have to start building AMM with a better payload but be less accurate.

At least there are things to consider.

You know... that gets me thinking.  Perhaps I could devise a counter-strategy to my missile heavy fleet.  33% engine tonnage (to be faster), lots of lasers and AMM, not a single ASM launcher.  Beam-fleet with AMMs gogo!
Yeah, totally different.  How much armour do your ships have?  My mainline missile ships have like... 3 layers.  >.>
And I don't ever use shields.  

I build my ships like glass cannons.  
=D  Totally different again.  When I decide to attack, I make sure I have overwhelming local force and then aim for strategic victory instead of tactical ones.  No qualms about launching against populations if I can't take the time to conquer them or if I deem it necessary for final victory.  
As for losing ships?  *shrug* Sacrifices are necessary.  And it's not like my ships are the bottleneck, it's the missiles.  

This is exactly why I like to rely on beam weapons as well and destroyers with faster engines. If my PD defences is enough I can just detach my destroyers and chase the enemy down and engage them that way. The problem when you face an "intelligent" opponent is that it is expected and you face a relatively balanced fleet in return.

A regular cruiser at ION tech era would have 5-8 layers of armour and perhaps 100-300 points of shields based on its size. I build ships to last and I like to protect my crew which I value greatly. I also use the highest available training rate so crew start with a 12% crew rate. Most ships have at least a 20% crew rate once fleet training is done and I build my larger ships to last for decades if I can.

I usually don't accept losses in anything but smaller scout ships. But I value human life (and alien if I can) above all...  

I don't think our economy is all that different actually... population is also a major concern for me too. It usually are a combination of wealth and population for me. I also seem to rely less on missiles than you in general I suppose. I usually keep a smaller but more powerful force of carrier/missile ships as my core and a large amount of smaller and stealthier surveillance and scout ship squadrons.

Once an enemy is detected my fighter/missile boats/missile cruisers overload the enemy with missiles in a few large waves of missiles. Once most of the escorts with AMM has been knocked out killing the rest with beam armed destroyers (that also act as my PD escort of larger task forces) is a piece of cake. I'm not even a stranger of keeping my destroyers in carries to increase the overall fuel efficiency of my fleet.

I almost never face active sensors at that range since they are so expensive to make and update and too easy to counter. If my main opponent used a size fifty sensor in my current campaign it would have a range of 480m km. Creating a missile with that range is not really economical as you pointed out and you are quite right about that. What I meant with range on my missile is to mount it on a platform to deliver it at a much further range to get under your active scanner range. This is not very difficult and usually require very little research.

In the above example I could simply use my carriers to carry my 3000 ton missile boats and slip right under that sensor and deliver the payload that way. In my current campaign I don't have box launchers yet but at 3000 tons and 25% reduction those 3000 ton ships could deliver a few salvoes of size 4-6 missiles (what fancies me) at a much shorter range completely undetected. A sensor with res 100 with range 480 would not detect a 3000 ton ship until about 35% of that range which would be about 170m km. So I would build a missile with a range of about 180-200m km or so. Not to hard with a size 6 missile.

If they used a size 50 res 5 sensor it would have a range of about 100m km. A boxed launched corvette at size 1000 ton would be quite efficient to deliver a size 4-6 missile at about 120m km.

In order to cover all it's bases the opponent fleet would have to use many different size 50 resolution scanners. Probably everything from 5,10,20,40,80 and 100 to cover all the bases. Problem is that a singe surveillance ship will know all the resolutions used and devising a plan to counter it will not be too difficult. Having a few options available from start might not be too expensive in comparison either. Each sensor above has an RP cost of 8000 which is quite expensive at this tech level, less so at higher levels though in comparison.

For that cost in research I would be able to get a few levels of cloaking tech as well.

Anyway, we seem to use a very different tactical approach to the game. I do everything I can to avoid my ships to be detected by the enemy to conserve resources from having to defend myself and I might also rely more readily on beam defences than you to be even more economical. I mainly use AMM to thin out really large salvos to decent levels and let Beam PD and shields do the rest.

In the early game when I still use missile cruisers (say ION tech) I usually have about 1 size 6-8 missile launcher per 1000 ton miniaturized at 25%, that is 100 ton launchers per 1000 ton ship. That leaves 900 tons for defences, engines, magazines and so on. The size of a cruiser is usually based on the maximum size of my ship yards so anything from 20000 tons to 50000 tons at this stage. These ships beam PD can usually swat at least an equal number of missiles with their beam weapons alone with a few AMM launchers to help with larger salvoes if necessary.

The teachings of Sun-Zhou basically tell us... know thy enemy and bring sufficient force to deal with him. If you bring the force before you know their strength you are putting all the eggs in one basket as they say. 
That is basically why I use my above strategy.

In general I would say that standardize ship speed and size can be somewhat a double edged sword against an intelligent opponent. To easy to counter with optimising weapons, sensors etc..
The one that can adapt faster to an opponent fleet composition will usually come out on top.

All in all carriers are much cheaper than most ships per tonage and so cheaper to maintain. I'm usually more worried about my wealth cost and that makes carriers very attractive to me. Carriers can also house ships much larger than a fighter.

My main concern is usually being able to launch missiles from outside enemy active range. If that means one billion km that will be the minimum range for those ASM. In my opinion you either launch and launch enough to penetrate the defences or you simply need a bigger salvo. No point in keep hitting your head a against a wall. Once you hit that critical mass that is necessary it is allways worth it, even if you have to pay a hefty price for that one salvo.

If you fire outside enemy active sensors you also don't need to waste much resources on AMM. So you can sacrifice some more on offensive missiles. Armoured missiles is also great for alpha strikes against mainly AMM and Gauss PD.

Also, big ships build faster per tonage so they refit much faster than smaller ships per tonage. I really don't find it all that problematic to build large Naval yards. I'm more concerned with my economy and find this a major cap on the number of ships I can have.
My experience tells me that a healthy balance of both small, medium and large ships is preferable.

How do you use size 50 as a scout sensor, these are spotted many billions of km away and alert every spaceship in the system to your position?

I know that larger sensors is cheaper then new tech at higher levels, but at active 31 they still cost the same as the tech you just researched so still pretty expensive.

when active ranges increase then strategies such as fighter platforms is highly developed as well and ship based missile platforms will tend to diminish in importance. Fighters can be used to strike fast and very far.
Or things such as cloaked ships is researched and suddenly you find that you need to drastically reduce the resolutions on your sensors to detect these cloaked missile ships.

I'm mainly speaking in games where you are up against a human opponent and not the AI.The AI can easily be tricked by most strategies.

I'm not saying that size 50 sensors are worthless either, they can have their place. But when you are hard pressed for research and are competing against other evolving empires then every RP has to be used efficiently.  As long as you are superior in tech versus your opponent I could See myself using size 50 active sensors, but I would spend the RP on lower resolutions first. Just my personal preference.