On GP each barrel hit should increase its damage by 20% per barrel

I'd be ok with this if the barrels got a pretty large damage nerf as compensation

Hopefully you would reduce the damage for one barrel from current, because they already do hella dmg

yes, because his barrels need to do more damage

actually i think this would be good for ignoring the armor.

so like 1 barrel ignores 20% of armor 2 barrles ignore 40% 3 barrels ignores 60% 4 - 80% 5+ - 100%

You mean, because gangplank needs to do more damage?..

On GP each barrel hit should increase its damage by 20% per barrel

With changes like this, it's worth considering the general mindset of LoL players due to how LoL plays out.

Kha'Zix's isolation damage doesn't look like bonus damage to anyone, it looks like a condition Kha'Zix needs to reliably perform to function properly. Rapid Fire Cannon's passive doesn't look like a nifty bonus to ranged champions, it looks like an item that's almost completely useless on a melee champion (despite most of it's cost being Crit and AS).

A big part of LoL is about optimizing and getting the best possible result, and not being satisfied with the 3rd best outcome. If GP's barrels increased in damage per chain: big chains would cease being something that looks cool and feels good in the right moments, and become something that feels like THE ONLY WAY Gangplank should be played.

gp doesn't need any more damage from his barrells, if anything they should be nerfed

Sure but only if they now cost 120 mana a use