nope it just degrades from 100 to 75 to 50 to 25 and on 0 it breaks won't break randomly i'm guessing you mean the handcannon by any means wich is relieing on your firemaking level
I do not think it breaks randomly, but if you die with it, and lose it, but get it back from a gravestone it will go to Karil's Crossbow (0), but all barrows items do that. As far as pking goes, I prefer the rune x-bow as it hits harder, but Karil's is faster, so I'd say mainly preference.
It takes 10 hours of combat to fully degrade that's a long time, plus its not too expensive to repair it, I think its like 100k or so with 1 smith/having a ncp to fix it. If you have higher smithing you can use the armour on an armour stand in your house/someone anothers house.