How can you be certain the sprue is straight down. Heck - trying to get it perfectly centered straight up is a challenge sometimes, even though you can see it. I doubt very much anyone can get it straight down and centred. Matter of fact, I'd put money on that. So- if it isn't centered perfectly straight down, then the base of the bullet is wonky - out of balance and cannot shoot as well as a perfectly centered ball with sprue up. Roger is correct, the base must be perfect - well known fact & not fiction nor imagination. Saying you can get the sprue straight down is fiction.