I was teasing you JD, don't be so defensive, I don't know anything about Hi-points except Nonya gave you a bad time about them, never touched one, no one around here sells them, so I've never even seen one, I considered buying a pistol last year, but I couldn't find one to check out. My point was that you were used to shooting pistols, doesn't matter what make.
Groups are measured center to center, but since that's not easy to do, measure from the outside edge of one to the inside edge of widest holes in the group.
Sounds like shooter error, but read the Handi Basics 101, those will help you get the best groups since the Handi isn't a bolt gun and needs some specific shooter input for consistent accuracy, like pulling the trigger all the way to the rear and placing the forward rest under the hinge instead of further out under the forend. How you close the action as well as making sure the gun is placed on the bags the same each time is just as important.
Shooting the rifle without the forend on it will tell you if the forend needs work, the 3rd shot flyer could be heat related on bigger cartridges, but not normally on a .223 from a cold barrel, but if it was still warm from previous shooting, it would apply.
BTW, wall nuts as in Black Walnut is just one word.....unless you have something called wall nuts I'm not familiar with!!
Tim