Hmmm, thinking about Fulvano's Blunderbuss, I bet that Charm chance (5%) is per pellet hit or crit - not per shot hit or crit. That's how Silver Flash works with Divine Mark, meaning that the chance for it is higher than you'd expect.
If I remember high school statistics correctly P(at least one Charm) = 1 - P(all Charms miss). If we assume all the 6 pellets of the Blunderbuss hit or crit, then P(at least one Charm) = 1 - (0.95^6) = 26.5% Charm chance.
Not sure how useful it would be, seeing as guns are painfully slow to reload, but it is pretty neat. Might form the basis of a Swift Aim Charm Ranger perhaps (you wouldn't even need high Might, just max Dex, Per and Int and let the frequent Charms and hungry pet do the work for you).
Edited by Jojobobo, 07 December 2017 - 10:07 AM.