Look closely as most old English .410's were for the 2 inch cartridge. Easily obtainable here but not, I believe over your side. The .410 was only ever intended as a specimen collectors gun for shooting things for taxidermy until in about 1913 BSA brought out a bolt action gun based on a Lee Speed .303 action and Eley started making 2 1/2 inch ammo for it. If it doesn't mention the chamber length then chances are it is a 2 inch. Can you say what sort of gun it is and post photos of proof marks?
If it is 2 1/2 inch I would avoid U.S made ammo as that is intended to function in semi autos and has a quite high pressure. A friends semi auto Remington 1100 that will cycle 2 1/2" Remington and Winchester stuff won't cycle with Eley and Lyalvale 3"!!
Like to see it Greg. Can you get European .410 ammo there with the CIP mark? Lagopus.....
