Huvius, first, I use my .500-.450 #1 for hunting most. So absolute reliability and easy loading require full length resizing anyhow. As both barrels are a bit rough, I did not have much luck with greased lead or paper patched bullets, but the load mentioned above, using jacketed bullets, shoots inside 3” at 100 m all the time. Before you tell me recipes for any cast bullets, I got an entirely different problem to solve now: We are ordered to use only lead free bullets for hunting in our state forest! So I will have to develop a leadfree load, maybe using Barnes .45-70 350gr bullets, to keep my rifle in action.
Headspacing off the shoulder was out in my rifle, as both chambers are very slightly different. Sorting and marking cartridges for right or left is not practical for hunting use, so I have to fl resize anyhow. I regularly anneal cases and have had no losses so far.
My case necks expand from .479” outside diameter, bullets seated, to .492” after firing. IMHO this .013” = 0.33 mm neck expansion is not too excessive. Alas, any case neck has to expand on firing to release the bullet. Lack of space for neck expansion is the main reason for excessive pressure when a 8mmS, .323 bullet cartridge is fired in a tight 8mmI, .318” bullet, chamber. Contrary to popular belief it is not the too small bore/rifling dimensions.