If my best friend said I just loaded these, I would give him a thorough round of questioning before I put them in any of my weapons. I personally would pull the bullets, weigh enough of them to get a basic idea of their weight, throw away the powder, keep the primed cases, load the cases with a KNOWN powder and use them for practice. If you feel comfortable with the bullets, run them over a chronograph, get some information using inexpensive bullets.
Saving an unknown powder and "building" a load based on a guess is a quick way to damage or ruin a barrel not to mention an action. You can buy an awful lot of powder, even at the price of powder today, if you ruin a barrel, action or take a trip to the hospital.
Now think about the explosion that going to happen only inches from your eyes, face and head.
My two cents worth, after reloading for over fifty years, of my opinion. Grain of salt should also be taken with my opinion.