The Rem XP100 in the photo is someone's designer gun or one of the many calibers it was offered in in later years. The original caliber was Remington .221 Fireball, which was a shortened version of the Remington .222. I had one in the late 60's and it was a PITA to reload cartridges for because one had to use adjusted dies for either a .223 or .222. No one had dies for a .221 Fireball to my knowledge. The new cartridges in a box were virtually unobtainable because it was the only pistol on the market that chambered this round.
Any other XP100 pistols in any other caliber are simply not XP100 pistols in my view.
Kind of like the new wave bling for 1911 .45 ACP pistols which look nothing like the original 1911 guns nor the 1911-A1 guns from 1925 and cost $2K or more. Apalling.
Old dog here and I am off topic, as usual. Sorry.
Jim