From everything I know about chewed ball, they just don't seem to work in a rifle. How well they work, or don't work in a smoothbore will always be an open debate. In my experience, with my smoothbores, my loads/patching/ball sizes, and in my limited testing, I think there is some truth to a chewed ball flying a little straighter. But there are so many variables that it is a hard thing to prove or dis-prove. I'm on the side of "it can" produce a tighter group. Depending on a million different variables.
I would not spend (waste?) the powder and lead to try it in a rifle. The only reason I can think of to do so would be with a very undersized ball, if that's all one had. Chewing (rasping) the ball does increase it's diameter a little, it will almost take it to the next size up. (.570" to .575" for instance) (it takes my .570's to exactly .575")