Novels tend to be rather dubious as sources considering how often they mess around with the power levels of things. The only thing I trust at this point for the most part is tabletop rules. And the Infernus Pistol is a weapon that one shots centurions. When it comes to the Inferno Pistol whatever you're shooting is highly unlikely to survive even a single shot or be in a state to fight if they somehow do, Space Marines are no exception. Of course the long time they apparently take to reload , very small ammo capacity (to my knowledge it's only 4 shots and you're empty) and very short range do make up for the fact that they are murdertastic.

Novelizations are the prime category when it comes to determining how something works/fares in 40k. If you want to use tabletop rules and stats then your chances at survival decrease marginally. Anyway, OP has final say on the whole situation.

Enjoy.

I dont mind if we attribute something to weapons that's not described in lore/novels (which often contradict each other within various versions of codices etc.), contradictions are inevitable so I wont mind if Victus's pistol will be powerful enough to lay a raging khornate down in one headshot )). I'm not the guy who can sit for hours, searching and comparing different codices in an attempt to verify some weapon's precise stats

If it couldn't it would totally nullify the entire reason he has it. A sniper rifle and a combat knife aren't exactly formidable against a light vehicle or another Space Marine (or similarly heavily armoured infantry), especially at close range in the case of the rifle. Hence the Infernus Pistol.

Ok as far as turrets inside the ship, highly unlikely. BUT they would have an armory. So heavy stubbers, heavy bolsters, autocannons, would all be possible to setup in different sections or areas of the ship.

Naval bolt Pistols and boltguns too. The Navy do prepare for the eventuality of heavily armoured targets. These ships are insanely hard and time consuming to build so obviously you'd want those defending it from boarders to have access to better weapons than las and autoguns.

And Rackham, is he, even clad in a carapace armour, able to battle chaos space marines in melee? Because in some point it seems he will have to

Yes, but the numbers would be limited. Placement will be key.

Yes he is in carapace armor, of course it's a higher quality do to his position of Lord Commissar.

@kanila correct me if I'm wrong but Carapace armour is good enough to provide some protection against most melee weapons as long as they're not a power weapon or something. That, and a plasma pistol and power saber are on the list of weapons capable of treating power armour like a tin can. The only real problem with the weaponry is that plasma overheats. Sometimes with catastrophic effects.

I would use Fantasy Flight books rather than TT codexes for RP-stats. But this is a subject everyone has their own opinion.