"Soft soldered"? I must have missed that, but it does not seem reasonable, although the total length of joint, and a fairly snug fit would make it pretty strong even if true.
There are grades of soft solder, just as with silver solder (which would be fine). Although, I seem to recall some English guns with the two barrels soft soldered together. Something about being able to separate them without disturbing other parts.
It's not so bad, you can get away from it if you need to.
I have Hanafin, Berg (Swedish), May (English) and Tiers (French, was Thiers) all fighting inside me! The Tiers and Hanafin gang up on the May, and the Berg fights and loots all of them.