You are entirely correct
Bas, some solder joints on double rifle scope bases do come apart. I have actually witnessed it myself on a friend's high $, best-quality Belgium Lebeau Courally double 9.3x74R over/under rifle. The expression on his face was priceless when the front claw mount came off the barrel as he was delicately putting his scope on the gun that morning!
In most cases, it is due to poor workmanship (too much gap in the contact areas, or cold tin solder, or not enough flux, etc.). There is no magic solution for gaps in the contact area but better matting of the surfaces before soldering. In regard to the solder itself, this is why I prefer silver solder over tin solder. It is much stronger. The issue - because there is of course no free lunch LOL - is that silver soldering requires higher temperatures. These temperatures are typically higher than what can be used on relatively thin double barrels, but they are compatible with the thickness of a bolt action, although one needs to be careful about not altering the heat treatment of the lugs, therefore use heat absorbing paste inside the action while soldering on the outside. Complicated...
Re. Loctite, for clarification I was not talking about gluing the bases, but thread-locking the screws that attach the bases, in order to prevent them from loosening. I was horrified coming back from Africa in August to discover that after 54 shots the 8-40 base screws on my .340 Wby had loosened from 35 inch/lbs down to about 10 inch/lbs !?!?!? Upon research, I selected Loctite 263 thread locker because it includes the primer necessary to use on non-active metals such as stainless steel (which my Mark V action is made of).
I am keenly interested in the result of your experiment just gluing rear sights to the barrel with Loctite 380. I reckon that if it holds on a .460 Wby it will hold on "anything."
Please DO provide updates on the developments... I can see in my future applications for combining gluing the bases with 380 AND thread-locking the screws with 263 (a belt & suspender type of approach, which I like when attaching bases on an action
