I have a Rolling Block in 250 Savage, 12 twist 25" heavy varmint contour barrel that shoots jacketed bullets a little over 1 moa.  It would probably do better if I could seat bullets closer to the lands but I swear I would need a bullet 2" long to reach!  If I were to switch to cast bullets and breech load there would be a gap between the end of the case and the base of the bullet.  Is that a recipe for disaster or something that might work?  If I were to set the barrel back and rechamber I think I would throw the barrel in the canyon and start with a new 10 twist and a thinner contour.  Thanks for any advice.  Tom