Hmmm, I use 17gr in mine but they do a 20gr, I've never tried them though! I don't get any more fouling than the lr to be honest too. I'm comfortable at 100 yards on a calm day, can't say about windy days, as I'm too soft to go out when it's windy. I'm sure a man of your standing could get another 30 - 40 yards, Errr I mean your friend! Come join us on a mouse hunt ?
Ps. I'd definitely recommend a mod too, the difference is dramatic. I'm using federal 17gr ballastic tips, they turn rabbits inside out at 80+ yards no bother.