Hey Harry, did not mean to imply mod the 850 to HPA,, Oh no, not too cost effective in my opinion. I really am not even too fond of adding the "Big Bottle" c-o2 to it, kinda takes away from an otherwise "clean" looking gun. The internal mods such as the hammer spring I think would be cool to bump it up a tad. Was just funnin with Ya cause I have been "bitten" by the "Dark Side" myself,, Thanks one whole he$$ of alot Gene, Kirby,Jon,Jay, & all the others that "Forced" me to shoot thiers last weekend!! GEEEEEZZZZ Tim.