I've been working on guns for some time now and have been using muzzleloaders for 15 years or so now, but I still am no expert. What I do is inspect the weapon carefully looking for defects in the barrel, such as deep pits missing peices of laminate, bulges and corrosion under the rib. Then if all that is ok I "proof" the barrel with 10 percent more than my max field load but I use 3f. I fire 10 of these remotely, carefully inspecting the weapon after each shot for any changes. Then I deem it somewhat safe to fire from the shoulder but I'm always inspecting it for chnges. Even then one might let loose on me someday, but I have shot thousands of rounds out of old guns and none have given loose yet, but you never know.