I’ve seen a few model 21s fail. I never noted what forearm was on the gun, and all of them were long enough in the past that I wouldn’t have paid attention. The guns failed at my club, and were guns shot by guys who used them a lot. Dewey told me that 4140 steel is tough to solder, not impossible, but, it takes more skill to get it right. The guns I saw fail were old guns back then, and Kirk told me he considered relaying ribs and fixing loose lugs to be regular maintenance on double guns, so, they were likely due. It has never happened to me, but, my doubles aren’t high volume guns, they shoot a clay game here and there, and go hunting.
Never have heard of a brazed barrel having a rib or a lug pop, but, not sure what a guy would do if it did. I would think it would be a tough repair.
Best,
Ted