I'll start.
My friend has a Tanaka Revolver and bb's were hitting the end of the barrel when he shot. So he did two things to fix this that have WORKED GREAT He is using .28 bb's
1. Completely removed the hop up all-together
2.Took out the stock barrel, pulled the barrel out of a cheap $40 hardballer shotty, cut that down to the right length trimmed the tip and put that in the Tanaka.
It's dead accurate, extremely reliable, with an insane fps