Probably already reported...but I searched and didn't find anything...
Disruptors III are size 8, cost 70, and do 8 damage.
The next tech in the line lets you build Subspace Blasters,
which are size 9, cost 100, and do 8 damage.
In the ship designer Disrupor III is listed above Subspace Blasters, because they're way more effective/efficient, even though Subspace Blasters are of a higher tech level.
Ie, the higher tech weapon is bigger, costs way more (when usually each bump in tech level is a 5bc increase, all previous techs are 70, 65, 60, 55 etc), and do the same damage.
The next tech after Subspace Blaster is Subspace Annhilator, which gives you NO new weapon and NO other benefits - that is, researching it does nothing for you except open up the next weapon tech in the line, which again, is very odd, it's the only weapon tech I know of that doesn't give you a new weapon, and the fact that it doesn't give you ANYTHING at all makes it pretty much useless (except to unlock the final beam weapon tech).
--- other comments... ---
Overall, I feel the pricing of engines and weapons is often very wierd. For example, you might have 3 variants in one tech node, blaster 1, 2, and 3, where they get progressively smaller and do the same damage - but the cost will be the same throughout. It would seem (somewhat) logical that the cost should be lower to begin with and ramp up as size decreases (pay more for efficiency) instead of being the same, significantly higher than previous tech level, cost throughout the whole node.
So, for example, instead of having all of laser 1, 2, 3 cost 20, and all of blaster 1, 2, 3 costing 30, you'd have laser 1, 2, 3 cost 10/15/20, and blaster 1, 2, 3 cost 20/25/30 - assuming, like usual, that the size decreases slightly as you progress thru the 1, 2, 3.
I guess it makes sense in a way - as you learn more of a particular tech you can do it smaller for the same cost (dunno if this mirrors reality, at least not always). But it sorta takes some flexiblity out of ship design, as you have less opportunity to sacrifice space to save on cost. Why use blaster 1 when blaster 3 costs the same and takes up less space for the same damage value? Your only option would be to drop down an entire tech node, to laser 1 perhaps, but usually the difference between two tech node levels is much more drastic for size, making it an unlikely choice.
And then there are the few cases where an item costs less, has a lower size, and is more powerful than a lesser tech item (of higher cost, bigger size, and lower power). I guess there are just some technological sweet spots.