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In the case of the .45 ACP, the maximum overall length is specified to load into a magazine and up the load ramp without interference. If you try to seat a blunt bullet shape out that far it won't feed reliably.
Since round nose ball is the orignial round, a good starting point is to take its OAL and subtract the difference in the length of the blunt round. This will put both the same distance into the case and leave you with the same powder space. In this case, 0.660"-0.615"=0.045". Subtract 0.045" from the maximum OAL recommended for the same-weight round nose bullet. SAMMI max for round nose is 1.275", so use 1.275"-0.045"=1.225" for your new OAL max. Try to get bullet within 0.010" of that length (in other words, 1.215" ±0.005".
It takes a whole 0.100" from recommended depth to raise the pressure of a ball load 3000 PSI, so you could use the 0.015" shorter Lee number without consequence.
Nick
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