Looks like a Jones style lockup which could be black, light nitro or full nitro.
Mike’s suggestion of weighing the rifle makes a lot of sense.
The only 577 I’ve ever owned was an Alex Henry double which, of course was a black powder rifle, but was a really heavy rifle.
Way heavier than a 500.
And, in the shooting, was WAY more powerful than a 500.
Unless someone is looking to turn a purchase and make a pile of money, I don’t see any desire to own a full house 577!
Well, that’s a little lie…. I’d like to have one but I don’t necessarily want to shoot one!!