...by sighting in with pellets and then using loose powder you had to get a different point of impact.
Actually he stated that he sighted in with powder and then tried the pellets.
You won't get a different point of impact with Pyrodex following the same procedure.
I am glad to hear that your Remingtom 700 ml does not get a double-bang effect. However, it is the first one that I've heard of that does not.