i have both double rifles and shotguns . in percussion and flint I also have a number of originals in my collection dating as early as 1832 .
Can you unseat the second barrel after firing one barrel . The answer is yes it can happen and its always best to check the off barrel .
Now that being said in all the years I have shot and collected muzzleloading SXS’s I have only 1 time found the off barrel un seated and that was do to my own stupidity of mistakenly double loading the powder on one barrel .
I also knew with the recoil that I had better check the second barrel . When I did I found it had moved but not more then about ¼ of and inch .
Our local group also often shoot clays with out muzzleloaders and many of the fellas also have SXS.
I think most all of us load both barrels and shoot two consecutive birds .
With the proper cards and wads , things hold real well .
Semisane
Is correct , just check your loads now and then tell you get to know it