The "bore riding" part of the bullet has more/just as much influence on accuracy than the bullet/groove diameter does. Cast a bullet or two, and see how the bore riding part of the bullet fits into the muzzel of your gun. It should require slight pressure to go in as far as the first band on the bullet. Do some reading at the Cast Lead Bullet Association's website.
Sometimes you get what you pay for, sometimes you only pay more for what you get.
Three shots are not a "group"...they are a "few".
If the Bible is the literal, infallible, unerring word of God...where are all those witches I am supposed to kill? (Exodus 22:18)