Not Rockite, but similar...
Rockite is the same thing as grout. I used Quikrete Construction Grade Grout. My stock started out at 23 oz. (About 1.5 lbs.)
https://www.dropbox.com/s/asfftwezd9...61935.jpg?dl=0
Doing the fore end brought the bare stock to 32 oz. (2 lbs.)
https://www.dropbox.com/s/467hdtbeea...62151.jpg?dl=0
I then did a full fill in the Buttstock. That brought the stock to 59 oz. (3.688 lbs.)
https://www.dropbox.com/s/stzkup6um0...61808.jpg?dl=0
Granted, Rockite is lighter, based on others' listed experiences. My gun is literally just under 12 lbs., with bipod and sling.