Factory 10 were not marked on this example. This is a NID, not exactly the same. But I do not doubt a 12 barrel has enough strength to pass proof for 3 1/2" chambers. Those were stout barrels, cannon like.
[Linked Image from images.gunsinternational.com]

But this is a true NID 10 Mag. and it does have the markings.
[Linked Image from images.gunsinternational.com]

And the EBay barrels in question. I would ask the seller to drop a shell into the barrels or measure the chambers.
[Linked Image from i.ebayimg.com]
[Linked Image from i.ebayimg.com]

Last edited by KY Jon; 04/16/22 09:58 AM.