I recently decided to level up a character centered around the Barrelsmith gun set and the most straightforward thing to do seemed to equip every other item with an item skill modifier for Grenado and Canister Bomb that I could (while leaving damage for both in the fire category). Currently my draft character looks like this although I have more resist optimization to do still.
What I want to call attention to is the way I now appear to be converting 300% of my pierce damage on Canister Bomb into fire damage.
Here are all the items with Canister Bomb modifiers
So with the goals of using Barrelsmith set, the Mythical Mask of Infernal Truth and Shard of Eternal Flame are pretty much the only options for Canister Bomb if you want to leave its damage as fire.
May I suggest changing the bonus on one (or both) of these items away from pierce conversion on Canister Bomb to something else? Flat damage, burn damage, conversion of physical to fire (to convert the internal trauma from improved casing) or even - skill cost? Perhaps move the pierce conversion on one of those over to Grenado?