will the copper discs in the PDX damage the full choke barrel?
I don't see how copper is going to damage the STEEL of the barrel.
Ammo makers know that at least SOME of the guns their ammo is going to be shot from will be full choke guns. The ammo is made to handle that.
if it wasn't there would be a warning label on the ammo not to use it in full choke guns!
The old .410 slug load was a 1/4oz slug doing a factory claimed "max" velocity, I've seen 1600fps listed. If we round down the figures, and drop a couple hundred fps from the claimed velocity (from a full length shotgun barrel) we get a roughly .40cal 110gr "bullet" doing about 1400fps.
What popular defense rounds is this close to???
Buckshot does increase the number of hits likely, but each pellet is lighter than the slug and will likely have less penetration as a result of that.
A single shot isn't the preferred choice for a defensive weapon but its better than no gun at all. Slugs and Buckshot are better than bird shot. I've shot slugs from a .410 Contender (10"), they are a pretty impressive round from a pistol. Never bothered with the buckshot in .410, myself.