I have an answer for you! The Neutron Gun isn't in the original Victory Streak (or covered in the Kilrathi Saga version) but it *WAS* added to the 3DO and Playstation versions of the manual. And here it is:
The neutron gun was specifically created as a weapon for medium and heavy fighters when the war first began*. It releases energized blasts of charged neutrons, drawing more power than either the ion cannon or laser. The refire rate for this gun is slightly closer, but the extended range of the neutron gun more than makes up the difference.
Penetration 40
Energy 15nJ
Range 4000k
Refire delay 45 sec
https://download.wcnews.com/files/manuals/Wing Commander III PSX - Manual.pdf
So what's going on here, anyway? It's a case of the writers behind Victory Streak wanting to tell a story that unfortunately didn't quite square with the final form of the game. If you'll notice, the Victory Streak specifications for the Hellcat don't list the Neutron Gun… the only place it shows up is as the Longbow's turret gun. So in their head it was a case of a logical story unfolding: the particle cannon was intended to replace the neutron gun and now a few years later it has. They expand on this a little more in the Victory Streak gun guide which claims they were used from 2640 to 2668* Unfortunately, the final balanced game ended up putting them front and center on the very first ship you fly!
* - I know, seemingly contradicting the Secret Missions copy protection which claims they were invented in 2618!
Totally - keep in mind that the manuals would have gone to print about a month before the final balance of the game was locked… so a LOT of changes to easily-altered, game-relevent things like ship and weapon specifications happened in that time, especially in areas where the player never actually 'sees' the number (like weapons). That's the cause of most discrepancies in the manuals and there are dozens and dozens of them.
The Sorthak in particular seems to have been massively nerfed. If you look at the 3D model the intent seems to have been to have four forward guns plus four dual-mount turrets (two forward, two aft). At some point, the forward two turrets were dropped entirely and the Sorthak became a whole lot less scarier. That's possibly due to the same ongoing issues with turrets/attached objects that caused a bunch of other last minute cuts of finished assets (including missile tanks, the triangular Kilrathi transports, more junk for the flight decks and Confederation frigates).