I was told that this stuff, which bears remarkable resemblence to Kitty Litter, is poured through a screen to segregate the 3F from the 2F. Next time I'm out at the range, I may try 3F and 2F with the same bullet over the chrono. I would suspect 3F would be a little faster; if for no other reason than it is a little denser by virtue of its smaller grain size.