Thank you for your replies. On the barrel is written
470 NE 500 GRAIN BULLET, on the barrle flats is written
470 NP and some numbers like 3120 indicating proof pressure.

I have a question on snap caps. I have ordered nickle plated brass ones for Century Arms in Ozzy. I there an advantage or disadvantage over using the common American available aluminum ones? I think my gun has ejectors, but since I have not pulled the triggers on the empty chambers, the gun only extracts the unprimed cases that I put in. Should the ejectors eject cases only after pulling the triggers and opening the gun to reload?

I also ordered a buffalo horn striker block that is used
to "let down" the firing pins against it when the gun is
broken down into the three component pieces. (the barrel,
the forend, and the breech) I have read that this is
another proper way to let down the firing pins which leads
to my next inquiry. Will the barrel fit back onto the breech
after the firing pins have been let down?

I did notice that to build a double gun must be devilishly
hard to do. Both barrels are tapered from the breech to the
muzzle and is connected by the full length rib that is
used to join these two barrels. The rib then must be
concave at the barrel joints and be tapered from the breech
to the muzzle also. To be soldered together the tolerances
and construction of the center rib is monumental compared to
the enginering and build of a bolt gun.

On inspection of the chamber area when the gun is open I can
see that the "Purdy third bite", that is located between the
barrels is made of a different piece of metal than the rib.
There are no joints between these pieces only in an oblique
light one can see the difference in the types of steel used.