Relevant quote,

The leading elements of Guilliman’s fleet started firing as soon as they approached to within a million kilometres. Broad spreads of torpedoes fanned out in intersecting patterns. Cannons hurled multi-ton anti-ship shells at the enemy. Such munitions would take minutes to arrive, and most would not hit their targets, but they were not intended to. Guilliman was closing off avenues of manoeuvre for the traitors with streams of explosives, forcing them into the positions he wanted.

• Dark Imperium by Guy Haley

On the surface it seems pretty decent range feat. But when you start thinking about it and actually analyzing it some things crop up.

The first thing we notice is, of course, the ~3 light second range feat. This isn't exactly inconsistent with a number of depictions of WH40k space combat. So it isn't all that interesting.

But then we look deeper.

It will take minutes for the munitions to cross less than one million kilometers. Assuming it is referring to two minutes and exactly one million kilometers this mean the maximum possible velocity of the "multi-ton anti-ship shells" is around ~3% the speed of light. This gives us a mass and a velocity so we can easily calc out a approximate kinetic energy, in this case assuming 10 tons per shell we get ~83 Mt per shell (assuming they are purely kinetic). Which would be... somewhat less than what many people would consider "anti-ship" yields in WH40k.

Both fleets are approaching each other so the muzzle velocity number is really going to be somewhat less than 3%c. This also follows that the ship's speed is going to be less than 3%c. This is a massive downgrade over the 75% c = attack speed quote that WWW can't seem to get enough of.

The next bit is that some of these (presumably unguided) shells will actually hit targets despite their one minute flight time. This implies some combination (likely no one thing was what allowed them to get hit) of poor sensors (can't see the shell until it hits), poor maneuvering (can't dodge the shell over a two minute lead time) or leadership (decide to take the hit).

This passage paints a totally different picture of what WH40k space combat would look like than what you would usually see on WWW.

What does it all mean for the purposes of this rant?

Firstly if you want to use a feat you should accept all the baggage that comes with it unless you have a really good reason not to.

Secondly, as is true with a lot of SF WH40k is inconsistent. There isn't a single "correct" interpretation you can make which won't be contradicted by several other groups sources. It is often best to think about these kinds of factions/settings less in terms of just "how strong are they" and more, "how strong are they on the low/middle/high end".

Thirdly, I get really suspicious of settings like WH40k and Star Wars Legends. I feel like I should see more quotes about things like firepower than the 5-6 quotes that usually get tossed around in threads considering the 200 books in both franchises. I have to wonder how many more feats like the above are in WH40k that just don't get brought up. Or if certain scaling some people do off some of the higher end feats is legitimate. This makes it hard for me to take people at their word when they say particular feats are the "middle end" or most common when I only seen the same six quotes. I totally understand it is functionally impossible for any one person to actually read through ever bloody WH40k book so it isn't like that is what I am expecting. It just makes me suspicious that people are reaching for readily available information rather than a complete picture that is all.

Edit: changed wording in one section to try to make it more clear what I am trying to say.