Thanks for replying Connor, most of what you have written here is what i wanted to hear.
i dont remember examples of blowing planets except planetkiller and nostromo incindent, and arent cyclonics a torpedo weapon, shot from prow or depends on source as usual? And something i forgot to mention- are there some missile weapons except torpedoes?
mainly its Nostramo and a few kinds of cyclonics (IIRC there was one torp that blew up a necron tomb world). There was also the 100- nova cannon bombardment proposed to take out St josemane's hope, although the context is a bit open to debate as to whether it meant mass scattering the planet or just decimating the surface (or the surface and the curst, or whatever.)
And yes cyclonics are mostly torpedo weapons - or at least, they get launched out of torpedo tubes. They'be been known to be launched from Cobra class destroyers, cruisers, battleships, planetary defence platforms (in context of anti-starship role, from the Bleeding Chalice Soul drinkers novels), and so on. And they can vary from 'planetary destruction' yield to 'take out a city' yield, and in quantity from 'single warhead to wipe out entire hive fleet' to 'large scale barrage of cyclonics patterned to cover entire planet.'
Heck there are even different KINDS of cyclonics - matter/energy conversion, radiation, 'raw plasma', and others, so they're not purely technobabble weapons (despite what some portray them as.) There are also other kinds of exterminatus munitions IIRC deathwatch mentions 'crust bursting' warheads for example.
i think my favorite form of Exterminatus was the antimatter bombs dumped into a gas giant setting off some sort of CME-like event to exterminatus a bunch of inhabited moons from Daenyathos - simply for the sheer excess of it.
And yes, there are broadside mounted missile weapons that are distinct from ordnance and torpedoes. Attack craft have their own torpedoes, missiles and bombs as well.
Its shame for me as a 40k fan since 2004 not to know it, but is a bombardment cannon some distinct type of naval weaponry or just a turreted macro cannon like these on broadsides? And where quarter of c stated(or calculated from)?
Bombardment cannons are turreted weapons (or spinal in some cases) primarily mounted on Astartes STrike cruisers and battle barges, although some dedicated planetary bombardment vessels, Arbites ships, and even Inquisition vessels have them. They're giant, turreted linear accelerators that hurl explosive payloads at the target. The speed stated was 'execution Hour', although in context that was in their 'anti ship' role. They can be used (effectively) against starships, but they tend to be shorter ranged than most other weapons. I believe they get a mention in the rogue trader RPG as well.
The HH novel 'fallen Angels' mentions bombardment cannon rounds being 5x more massive than macro cannons, and the BFG Armada stuff pertaining to the Hammer class Battlekroozers note that bombardment cannon, torpedoes, and nova cannons all have similar proportions.
As to the "averaged" projectile speed, i use as a guideline a statement from BFG, that "weapon battery shots cover tens thousands km almost instantly" including mentioned in BFG "mass drivers"
As a rule i tend to use that as well, especially if we're talking about the 'Age of sail' approach to loading and firing broadside weapons (good luck hitting a target tens of thousands of km away, moving at kilometers per second, and taking minutes to reach the target.) There's also the not-so-minor difference between ordnance and weapons batteries, but some people insist that only beam weapons have that 'instant' thing, and projectiles do not.
About durability- thanks for pointing at the ship s internal structure, wonder why i didnt think about it before.
Remember that even within a particular class (EG Lunars) there's lots of room for variation due to inconsistencies of technology and design. As a rule most 40k starships (or at least the really valuable ones) are not mass produced designs, so how they absorb punishment (and the degree to which they can) will vary. Case in point - the absence or presence of power fields as mentioned in (IIRC) Battlefleet Koronus as hull enhancement.
Concerning inconsistency- sometimes it can be a really good thing, cause allows that "personal canon" thing( for example, i dont like IA at all except some minor stuff and don t extrapolate these numbers to all 40k and even find some in universe explanation for not doing so)
As a rule I find it bad policy to 'pick and choose' which sources you do and don't obey. There's the obvious problems of cherrypicking, but the fact is not everyone ignores those sources and sooner or later you have to deal with them. IA books have lots of problems but a fair number of authors use the numbers and stats from them, and people will cite them as counterarguments.
And the last- can you advice some novels(except Execution hour and shadow point) with some interesting space stuff?
There aren't really any 'pure' Navy novels aside from the rennie ones. The only other one is the Relentless by Richard Williams, but that isn't so much 'starship fights' as it is just 'a day in the life of a naval crewman' from bottom to top. It can be interesting in a way, but you don't read it expecting another bfg novel.
Most 40K novels have some smatterings of starship combat, whcih is about all you can expect. The ones mentioned are probably the most 'battle heavy' - Dark creed and Dark disciplie both have it. sabbat Martyr and Salvation's Reach from the Ghosts is fairly heavy in it. As is cadian blood (IG novel.) The first two gray Knights novels have lots of ship to ship combat (at least the first one does towards the end.) The ultramarine novels warriors of ultramar and chapter's due have ship to ship combat.
the space marine battles novels gildar rift, Battle of the fang, and rynn's world also have some ship to ship stuff, although I'm not sure the brief stuff would be worth it except perhaps Gildar rift, where it's more prominent.)
Horus Heresy has a fair bit too. Battle for the Abyss is filler, but almost completely starship stuff. fallen Angels has it. know no fear has some ship to ship stuff as well IIRC. as does deliverance lost and flight of the Eisenstein.
other than that there is LEt the galaxy Burn which has a few 'naval' oriented short stories - two gav thorpe ones about a marauder bomber squadron, Andy Chambers' ancient history, and i think one or tow others.
Oh and there are the Andy Hoare Rogue trader novels - Rogue Star, STar of damocles, and Savage Scars. the range and number data is a bit weird (it makes World war 2 warships look long range dfor the most part) but its space combat.