Given the weight of the .500s in the newer rifles (Heym, Merkel, etc.), I don't disagree with that. They thwack you pretty hard. The .470 is definitely more shootable in those rifles. Even in .470, look at how many of these 10 to 10.5 wonders end up with recoil reducers in them - they're just more than most can handle. If you're set on the .500, don't do it unless you can shoot one of the make of choice before you bite.

Personally, availability of factory ammo is no consideration at all to me when I'm shopping for a double rifle. Most of us DR shooters never shoot factory ammo anyway. If you want the most out of your rifle, you'll be shooting handloads.

Either way, the Heym is a fine choice.