I have non-destructively over-pressured a few rounds following the myth that jacketed data applies to cast. I believe some powders are higher risk than others. Look at the max charges for 158 grain cast and jacketed bullets in the Western Powders manual (image below) - jacketed can use significantly higher max charges, or not. For AA#9, the starting charge for Hornady 158g XTP is the max charge for the 158 grain lead SWC. Case capacity and OAL do not fully explain this discrepancy. For AA#7, cast and jacketed 180g have the same max charge.
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Lyman’s 49th manual (not shown here) even shows various cast bullets of similar weights can have significantly different charges… but only for certain powders.
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I hypothesize that lube grooves & cannelures affect the torsional stiffness of a bullet, which may cause increased drag in the barrel (and therefore lower velocities at similar/higher pressures). I also hypothesize that a powder’s burn rate is dependent on the pressure, and that this dependency is stronger & weaker for different powders. If the relationship between burn rate and pressure is relatively weak, then you can more safely use jacketed data for cast. If the relationship is strong, then all bets are off. I gage how strong this relationship is by collecting load data for a bullet weight & powder from multiple sources and reviewing the range in max charge levels - big range = big risk.
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