Given that the weapon never turned up in any form beyond that rumor, it is probable Apollyon's Shootist having a super weapon is merely a canon-rumor and a false one. At least canonically, even if IRL there was some intent to have the 'Mech mount a "super weapon".
Otherwise, the Word of Blake would have either produced more of the weapon probably, or the Republic of the Sphere could have developed something from it.
I'm not saying BT hyperspace tech can't be weaponized (it can be, in several ways, though none so far are particularly direct or efficient or effective enough to bother), i just figure that it is unlikely the Word of Blake managed that and left it at one prototype weapon for one warrior, no matter how important. Everything else they did was used in larger numbers, even if they weren't very high, and this includes expensive tricks like super-Jump which wrecks the ship's (expensive) jump drive.
I'd imagine what happened was that Apollyon's Shootists sports "common" tech weapon but one that is somehow unusual (possibly modified), like how the King Crab KGC-010 sported unusual PPCs that lead to others think the 'Mech featured a new weapon system. Throw in some hypothetical concept of a hyperpulse weapon and you get a wild rumor machine working.
The actual weapon could have been, for example, a Clan ER PPC modified with an Capacitor, something that is quite late IS-to-Clan tech conversion, but it is plausible it could have been done earlier, if you'd care to spend money and expertise for it. Far cheaper than a mysterious superweapon, highly powerful, and possibly the kind of thing that takes just too much effort to use beyond a single example (especially since even the WoB wasn't swimming in ClanTech), whereas a HPG weapon could find use, if perfected, in just about anywhere.