You never said it was a factory choke. You said:
The shotgun has a 26" barrel with a "waterfowl" choke which seems to be roughly halfway between my other two shotguns with full choke and improved cyclinder
So the presumptions are:
The choke make is unknown.
You don't actually know what the rated constriction is. By your own statements you are guessing.
It is made for steel or other nontoxic shot. Pretty much a given for anything with a 3 1/2" chamber not made specifically for Turkey.
And I forgot to add that it is probably made for a specific size of shot range.
Looking at Remington's website the closest to what you describe would be the Wingmaster HD chokes. These are still specifically marked to their rated constriction.