Have you tried the H&N Grizzly 31 gr HP? My buddies gun loves them and that's what he shoots in it for squirrels. They shoot ok in mine out to 60 but past that they open up to an inch or so. My gun is power tuned and really likes the AA 25.4 gr pellets at 925 fps and up to 975 fps. However it is a little louder with them, kind of a loud snap. I am now shooting the 34 gr JSB MKI's at 915-920 and it is quiet and accurate.
Yes they are a little heavy, especially with a Discovery 30mm scope on top but I use a single point sling attached to the rail so it makes carrying a lot easier.