The owner of this barrel should take the lug and heat it up with a torch and see if the solder easily melts. If it does, then it is just soft solder.

Exactly, would be interesting to know if it’s low temp solder

I have a suspicion that it is. This is the second time in the last year I have hears of this happening. And by the look of it, it appears like soft solder.

I agree that it SHOULD be brazed. But that may not be how they made them.

If it were brazed as a repair, would the solder in the ribs come loose?

Yes bill. Unless a method were used to localize the high temp needed to braze it. Such as induction.

The heat required to solder the lug back in is going to be both a temp, and duration, that the ribs loosening is quite likely.
This isn't a simple fix, but a complete rebuild, and undertaken by anyone thinking it's a simple job is probably going to junk the barrels.

That's where the glue comes in.

It looks like they got the joint too hot & burnt the flux causing a weak joint. More that likely the repoductions were all soft soldered. And the reason we haven't seen more failures is most are shot very little, if at all. I've had 9 repo's over the years & most only had a few boxes shot through them, & then into the safe they go & a few were never shot at all. Most that come up for sale look like they have never been shot. So, this is probably why we haven't seen many failures.

Winchester 21 barrels are fully soft soldered. Making any work on them a nightmare. And they are supposed to such a great shotgun…

Hmmmm--I took a 20ga repro on an Argentina dove hunt and put over 10,000 rounds through it on that trip. The shooting was fast & furious getting the barrels as hot as they could possibly get from shooting which included opening & closing the action as fast as the bird boy could drop two new rounds in it and never had an issue whatsoever with the gun, let alone the lug coming loose.

I'm more of the thought that this failure is a standalone issue with this particular set of barrels and we shouldn't denigrate all repro's based on this one failure.