I went through this last year in my build, took forever, two different priming tools one from Show Cars, did not work for me, then I switched to 1/2" drill low torque and locked the switch on for an hour, came back and had it looking good, but it took a long timer, also what one of the other guys mentioned my rotating the crank helped, I must have been in a dead spot that was not oiling at that spot on the journals/weep holes.
I still never seen great oil, until I fired it up and then it came right up to pressure.