I intend to do the following unless someone has a better idea:

1.Obtain some 303 British Enfield brass
2.Fire form the cases so they're the correct size albiet a little short.
3.Load the cases full with blackpowder.
4.Crimp the heaviest 10mm bullet I can find in and start from there.

Thanks for the info PWM but I expect there's a safe smokeless equivelent to the black powder load. It's just going to take a little digging.

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