There are 8 M21 double rifles in the upcoming Julia auction. They were built by CSMC and have consecutive serial numbers and are in Grand American style. Quite impressive.
I didn't realize CSMC built big bore double rifles but they obviously did---the 470 nitro express is the largest caliber.
I recall Winchester built a few double rifles and there was one in the Cody museum a number of years ago---may still be there.
Have a look see and try not to drool.

Saw one at the Baltimore Antique Arms Collectors show today. Had a set of 20
Gauge barrels as well. Could have been mine to a mere $23,500.

Sadly, I passed on the opportunity.

That's the trouble you see a beater up for sale thinking to yourself, he'll never get what he's asking, then look again later and its gone.

A lot of people out there love those guns. It would have been my perfect waterfowl gun.

I'm surprised there isn't more interest in these fine rifles. Auction is Friday. I'll be watching the sale prices with some interest. I love my M21's but these are way out of my budget, not that it diminishes my interest.

Sorry, not Friday, but today, which is Wednesday. Bids on several of them were in the 17's, pretty reasonable for what they are. However, they may have been bid in by the owners. In that case, we may see them again. The .470 sold for somewhat higher price than the others. The John Durkin style B carving is a great feature of these rifles.

Thanks Eightbore---I got my days mixed up.
I'll check the prices when they get posted along with other doubles. The prices you mention are buyer friendly but seller unfriendly.