You really must give special attention to the rate of twist in your barrel, then go from there. Not familar with the 451, but my 504's have a 1-20 twist and shoot 460 NE bullets very good with 85 grainsof 777, with a #11 primer cap. From my experience 209 primers offer no advantage other than helping to cause a crud ring. I sighted my White in at 140 yards and the group was less than 1-1/2 " with most touching and the extremme spread was a flyer that was human error, if not for that the group would have been under an inch, Nothing like being a dirty White boy./