In 1957 Winchester's heavy 3" 12ga load was 1 5/8oz standard was 1 3/8oz. Your model 21 was most likely made around then or before. Those new Long Beard shells had I think 1 7/8oz plus buffer . Hope they had nothing to do with blow-up but it's a thought.

Well thanks for that info. Wish I had seen this prior. Never even gave a thought to the amount of shot. I am going to reach out to Briley to see what the cost of shortening with screw ins will be. But I definitely am on the hunt for long barrels to replace. Probably a hard find.

The original 12-gauge 3-inch Super-X load of 1 3/8 ounce of shot was introduced circa 1924/5. Western Cartridge Co. introduced their Lubaloy loads circa 1928/9. The 12-gauge 3-inch Magnum load with 1 5/8 ounce of shot was introduced in 1935 along with the Winchester Model 12 Heavy Duck Gun. In the January 2, 1958, Western Cartridge Co. price list. the Olins introduced the 1 7/8 ounce 12-gauge 3-inch Magnum load.

Attachment 83767

A bit of real trivia -- From its introduction the Super-X 12-gauge 3-inch 1 3/8 ounce load (P37) was just that and the Super-X 12-gauge 3-inch 1 5/8 ounce load (P38) was the Magnum. February 19, 1952 --

Attachment 83765

By 1953, Western Cartridge Co. was changing their load symbols and along with that the 12-gauge 3-inch 1 3/8 ounce load gained the Magnum appellation. January 16, 1953 --

Attachment 83766

The barrels are toast.
The only way they can be salvaged is to cut them back to before the damage and have a shorter barreled gun. Or you have that one tube sleeved with a new tube.

You may be able to get replacement barrels made and fitted to it by Galzan. They do the model 21 service today.

Sorry this has happened to your classic Winchester! This just reinforces my conservative shell selection for my prized shotguns!

people add barrel length to guns all the time...these card shooters have some really long barrels...most with added length to other barrels....as you say most all welders would not put their name on this work but also I do not know of a gun smith who will tell you this gun is fool proof and want blow up....I bet you could shoot 2 ounce loads through this set of barrels with them cut off and fixed with new chokes till you got tired of buying shells with no problem to the barrels..i m sure there is some model 21 shooters out there who have shot plenty of magnum steel shot oy there with no broblems to the barrels...I have a lc smith long range with 32 inch modified chokes both barrel that have shot boxex and boxes of heavy magnum loads with no problems with the barrels...no streaking of the barrels and no problems with the stock I did glass bead the stock before shooting these magnum loads...charlie

Shot Bridging
 

My two cents is this was shot bridging, since I see they were number 3s. The tungsten matrix is hard; tungsten by definition is harder than steel even in the matrix blend they make. And with a heavy wad with thick walls, when going down through the .032 choke there was no give and no shot deformation as with lead. The shot in the column formed a solid block and the walls like Jerico came tumbling down under the stress. With 4s, you may have gotten by, with 6s probably 99.9% of the time. With 3s or larger, disaster. With a more open choke, you probably get by. Remember with steel or harder shot, an IC shoots Mod., a Mod. shoots Full, and a Full shoots Extra Full and a thin barrel lets go.

Remember if you cut this back two inches, you are probably in the very thinnest part of the barrels, and there may not be enough metal to install chokes. so measure or have them measured to see how thin they will be where they will be cut. I think having the left side retubed is going to be the best bet, by somebody like Kirk Merrington.

Keep an eye on EBay. I found a set of 28 in Atlas Arms barrels with chokes installed for a ridiculously good price. I had them fit and use them as my upland barrels.

ja s opion is the best one yet...retubeing will make the gun new again....if you cut the barrels and can get new screw in chokes put in her it may out shoot the 32 inch barrels....charlie

Man I do appreciate all the responses to my unfortunate problem. I do love this gun and it has some memories. I shoot RST in every other double I own, but this one seemed to be my most modern double. Never worried about it. I used it at Hausmann's last year on the Nash Buckingham Bo Whoop shoot. No issues. If I get this gun back and up to speed, I will need advice on what to shoot - not for clays - but for serious waterfowl and turkeys. Otherwise I will go back to the Benelli SBE - and I really don't want to go there.! Seriously thank you all for your response - no where else on the planet for any real/honest/knowledge based information. So glad I am a member. And very glad this wasn't a Parker. 21s are reputed to be super strong. Cie La Vie. Thanks again