John, yes it looks like a Heym sidelock, and the cartridges look like 500NE.
A very nice double for sure.
It's interesting that it has ported barrels.

I agree that the videos are nicely done.

Yes, it is an .500 NE and an Heym.
It is an 88 safari, super luxus boxlock (they have real sidelocks too) with "blades" for more engraving.
Peter dont like sidelocks, because he see that the wood of the sidelocks aber to weak for an hard use in Afrika (in the summer he is there more than 4 months in an row).

Best wishes.

The "J.