If it accepts 410 commercial ammo it's been reamed out after being sold out of service.

I used to have a 1913 LSA No 1 Mk I** IP that was converted to 410 Musket in 1935. It had been reamed out to accept 3 inch commercial ammo.

I currently have a 1917 BSA No 1 Mk III* converted in 1936 and still in its original 410 clambering. Have been working on making my own ammo for it.
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