You can do a lot of accuracy studies, and determine it takes a very accurate rifle to determine that dirty primer pockets cause fliers, if you can prove it at all. In fact, most of what I have read and seen myself over time is that it don't make a difference. What you are describing, a rifle that is "two grouping" is quite common amoung Handis. With my 44 and cast, the better my bullets fit the bore the less of that I saw, I didn't do a lot of work with jacketed, but what I did seemed to point toward bullet weight being a factor, the heavier the bullet, the less two grouping I saw. The questions I would have about this center around the load, what powder, what bullet, what approximate velocity (exact if you have a chronograph) Two grouping can also be indicative of the repeatabililty of your rest. The more consistant your return to the rest; the rifle in the same place every time, held the same for each shot; the less of this you see. It can also be a sign of bedding problems. Do a search on "oring" or "oring fix", I simply don't tighten my forearm down hard, always leaving a slight bit of "rattle"