"Proofing" the gun yourself may not assure you of anything, and may actually damage the gun so that it blows up in your face faster, using normal loads. I do NOT RECOMMEND you "Proof" the barrel.
If that weld is suspect, putting high pressure loads in the barrel will just accelerate the stress on the welds.
These were junk guns- wall hangers-- back when they were sold. No one seriously used them for shooters. And if they were fired, they were shot ONLY with PRB and powder charges that would not exceed 60 grains of FFFg GOEX BLACK POWDER.
You are proposing loads with higher pressure, hotter burning substitute powders. DO NOT USE THEM. Reduce the substitute powders by 15% by volume, to be safe with them. That would mean a maximum charge of 50 grains of a substitute, to be equal to the 60 grain charge of Goex FFFg powder.
Send it back, and get your money back. You can find much better firearms, even used, for the same money, or for not much more. Safety is ALWAYS an issue with Black Powder guns, and I believe you understand that. What you need to understand that these cheap guns do give way, and have. They don't get stronger with age! :shocked2: :hmm: :thumbsup: