Rubber should make a big change, inner barrel will help.
Pretty sure banana has a 6.01 in there. You should pick it up straight from japan, yen is low so pdi stuff is cheaper when converted, X-fire or something is their official distributor.
I run 0.25 on my pistols, I find they are the sweet spot, for cqb anyways.
http://www.x-fire.org/etop/01_h.html
Shipping is cheap too.