I've pushed 145gr PB to 2k fps in 300BO 18: 1:10 carbine. Used WD 1/2% Cu alloy. What did I learn? Base has to be near perfect. I tried hard to leave no divit or bump. BUT the base wasn't quite square with the body! Showed on the target (100 yds) - as a circular 1 1/2" group. Consider the psi pushing on an angled base = worse angle base. And leaving the muzzle, unequal muzzle pressure. How does this apply to low pressure loads with softer alloy? Base cutting when casting. My tough alloy was hard to cut, sprue plate raises when cutting. Brings up the question of hitting or pushing the sprue plate open. Devil is in the details.
