it remind me of old youtube videos about spoon killer or something. he kills by hitting people with spoon too much work and the technology requirements are too high. electricity technology is very easy to develop, just make a simple motor to start with. and if there is magic in that world, just convert mana into electricity. btw what does liquid hydrogen do?
Super cools whatever it hits though as soon as it hits anything above it's freezing point then it quickly becomes a gas. Never had those science demonstrations where the presenter shows you a crate of liquid, then randomly splashes the contents at a viewer? the viewer stays dry but they feel really cold because the hydrogen rapidly absorbs the heat in it's immediate vicinity and goes from liquid to gas in nano seconds. (huge chance I botched the explanation)
And the ULTIMATE,LEGENDARY,MYTHIC,sure kill,best torturing weapon. Bring Gigantic speakers and large screen and a laptop. Make them watch Boku no pico while playing justin beiber songs
physical rounds work too, just make sure it's a shrapnel round that is coated in a non lethal poison that leave an itchy/ burning sensation. the more they writhe the greater the damage!
That's a topic for another conversation, now back to the armaments... A disposable wave dagger with a blood letting groove engraved on it, stab it into a target, the tip and a quarter inch breaks off staying embedded in the target, have it coated in a light anesthetic so the target does not feel it, and let them go, if done properly the target will steadily bleed out.