I based the 253m/s off a study of a period-accurate early lead-ball flintlock pistol. Where the early flintlock musket in the study, also period-accurate, attained 414m/s. So definitely closer to that hydrostatic shock marker minimum for the fish-periment.
Though, honestly, I should probably have gone in on Matchlock for earlier time-periods, I think it's safe to say the speed was within a reasonable area because of the minimum speeds required for lethality and the inherent force of gunpowder not being insanely different between the 1300s and 1600s. Y'know, as compared to modern gunpowder which is higher quality in the exclusion of impurities and much more precisely measured in it's chemical composition than an early Renaissance alchemist might have had.
Whether they "Needed" them or not, they had side-arms for a reason. And had them in previous battles, and battles before those, and battles before those. Feudal Lords didn't hand their well trained archers a bow and say "If the pike men fall, you'll just have to die, I suppose. No additional weapons!"
Very possible on the artistic license. Could also be that some of those archers figured dual-wielding was worth the Feat.
I wrote the following before you posted, but you posted before I hit post. <3
Honestly... Carrying a bayonet in a leather sleeve then dropping down and taking the time to install it on the end of your rifle is just... dumb.
It would make -way- more sense to just carry a proper melee weapon on your side in the space that bayonet is using.
I'm starting to think maybe the "Real Reason" for the bayonet rather than a side-sword is simply "The damned fools keep dropping their expensive muskets into the mud and ruining them when they draw their side-sword. How do we stop them from doing that?!" and that became "What if we made the side-arm only half as useful on it's own but make it -very- useful if you affix it to the musket so they'll hold onto their musket when melee is joined?"
"You're a genius, Jenkins!"