There's some debate over that - the Mk.I through Mk.IV were built for the old black powder load, but many were retrofitted with Mk.V style cylinders, and even the ones that weren't were used with smokeless ammo in service without any problems. Now, the Fiocci stuff IS fairly hot, but a Mk.V or a Mk.VI will handle it no problem - I've put lots through mine. It's ridiculous to think they'd make Webley ammo that couldn't be fired through a Webley.
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