When im target shooting i clean the plug every 3 shots, a few minutes in between shots to allow barrel to cool down.

Climbing shots for me have always been due to barrel heat.

I personally think you should up the charge to 100gr and maybe even 110gr. I know its a lot for 50 yards but if you want to put a smile on your face, thats the charge that could really do it. I haven't bothered with any charges under 100gr with BH209 unless i am starting off with a new gun.