Hi Doug, Welcome to the forum! It's always nice to see a previously unrecorded Navy. If you email me I will send you a link to the full Navy List which has all known Imperial Navies, some 1,500 guns. There is no orphan magazine #4233 listed (Navy mags do not have suffix letters), but there are several that are close.
May we see close-up photos of the proofs on the left receiver and the barrel serial number?
Thanks, Norm
normrab@comcast.net