My 2 bob's worth:

The problem is that the rifles were regulated to the ammo, not the other way around. As soon as you change from MkVII ball with its flat base and little aluminium filler plug, AND a cordite load, all bets are off downrange. The North American manufactured WW2 and post MkVII presents some challenges but if topped of with the correct bullet these are not insurmountable.

Thus we are presented with a couple of challenges. Firstly; how much decent MkVII ball has anyone seen lately, and secondly; if we fall upon a stash of Kynoch or similar, and then don't clean our nice barrels properly, they will "demise" rapidly.

The factors that change when you feed it anything other than MkVII include: bullet jump, pressure curve, muzzle velocity trajectory and all those interesting multi-mode barrel vibrations.

Bullets seated to a shorter overall cartridge length may cause feeding "issues" as well.

Try to stick to flat-based projectiles in the 174-180 grain range. Avoid boat-tails like the plague to minimise gas-cutting at the throat. Because of the way it upsets as it enters the throat, the open-based MkVII ball projectile provides a better gas seal than ANY conventionally-jacketed "sporting" projectile.
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