I have a Cogswell and Harrison double rifle that was built in 1886 that the factory record says is a cordite rifle; Here is part of the factory record:

This rifle was produced to an order from our New Bond Street shop and was completed by our craftsmen on 30th January 1886. It was built as a .400 cordite double rifle.

I didn't think that cordite double rifles were made that early. Obviously it does not have nitro proof marks.

Could this be a legitimate early cordite double rifle?