If the barrel was not ported, it would not have dumped that last little bit of pressure that was needed. If it was 1/2" shorter, the shot would look like your cartoon.
I was using a new (to me) non-canister powder, and what I do for such things is start with a survey of loads, hoping to find a reference min and max load. I loaded 3.2, 3.4, 3.6 & 3.8.
You can see what 3.2 looks like. 3.6 was very accurate in 4 pistols. 3.8 was also good. max is probably going to be around 4.2, but I won't bother checking. I have a good load for punching paper at 3.6
Last night I cranked out 2,000 of them.