The label on my bottle of 777 says reduce loads by 20% volume, not weight. I am willin' to take Hogdon's word for it. I don't like the groups I got though, but I'll keep playin' with it in my .50.
I can agree to that figure. What kind of rifle are you shooting? What kind of projectile? And how big a charge? Sometimes people try to push a projectile too hard and they end up getting terrible accuracy.
If your shooting a patched roundball, try putting a wonderwad under the patch to protect it from the head of the Triple Se7en ignition. I have to do that with one of the .54 calibers I shoot. It loves Triple Se7en but without the wonderwad the patch is smoked......