I had zero luck with the Berry’s 124 gr HP. In fact, such bad luck that I wonder if I just got some from a bad batch. Lacking a Ransom rest, I used to shoot quite a lot from prone to test accuracy. It was a confidence builder.

I’d say it’s pretty hard to pin down three things that are most likely to affect accuracy across the board in any particular caliber. In general terms, “quality never goes out of style.”

I would want a baseline to have some idea what my pistol (with me shooting it) is likely to do. You might start by getting a couple of boxes of good quality factory ammo and firing some control groups, being careful to be very consistent with your technique. Keeping good records is necessary.

In 9mm factory ammo, my first choice is Federal 147 gr. FMJ-FN, but some guns prefer lighter bullets, so I’d also be looking for a high quality 124 and 115 grain factory load, too. It’s nice to try to work with ammo from the same lot, so if you find something that works for your baseline load, get a reasonable supply of it.

Once I had some idea what weight and shape of bullet the gun seemed to prefer, I’d go on from there. I’ve had a hard time telling a difference with various primers in 9mm. A chronograph may help you sort that out, but probably only if you’re working with new brass. I think the powder selected often has more effect on accuracy in service grade pistols than a particular primer does.

It’s not at all unusual for a load to shoot very well at pistol (short) range that the chronograph indicates is not optimum, and sometimes one the chronograph shows to be very consistent does not shoot all that well. One never presumes the chronograph tells the whole story.