For optimum cast performance, you'd need to open the cylinder throats to at least barrel groove diameter, however, it will degrade jacketed accuracy slightly.
Since you want to use Linotype metal, here are my recommendations. Get a 432 diameter mold and if the bullets will chamber when not sized, size them to .432. The bullets should be water dropped to obtain optimum hardness, and with almost all lino, higher hardness, when water dropping, will be obtained if at least a little wheel weight metal is added. This because WW adds a little arsenic which is necessary for heat treatment, but is devoid in most lino. If you get hardness to at least 20 BHN, the bullets will spring a good half thousandths inch after running through the tight throats, and fill the barrel well. If you get leading with light to moderate loads, due to a small amount of blowby, increasing the charge to near max should fix it, whenever your load reaches a point which obturates the bullet base. If you can't chamber the 432 bullets, you'll have to size down till they will chamber, but if you get a 260 gr LFN it should chamber easily even when a bit oversize. I'd recommend that you go to a 280 gr for better accuracy though.
