Why not load up some 1900 spec 303 rounds?
They will work just fine.
I have a Marini with Metford rifling and another with Enfield rifling. They both shoot factory ammo and hand loads just fine.
Your Lee Metford rifle is strong enough for modern commercial 303 Brit ammo.
You might even find the fouling easier to clean with the rounded corners of Metford rifling.



























