After putting in some time assembling a heavy-barreled .223 bolt rifle, I finally got to the point where I was ready to shoot it, see what it would do.
I had some bullets from my previous .223 left over, 68 grain match BTHP bullets which I loaded to a moderate velocity. There were no firm expectations, just hopes. - But I was unprepared to see it shoot all over the target at 50 yards, not really what you could call a group. Then I peeked through the spotting scope and saw the key-holing.
Back at the shop, I belatedly measured the barrel's twist rate, and found it was 1 in 12 inches. Well, that explained the key-holing with the heavy bullets!
So I ordered bullets in 40, 50 and 52 grains. When they came in, I tried a few different powders and loads for each, and a clear trend emerged... The heavier the bullet, the more accurate it was, and the less sensitive about the load. The 40 grain bullets never did shoot well with any of the loads that I tried, but the 50 and 52 grain bullets did fairly well. The 52 grain bullets did best.
I ordered some 55 grain bullets that had done well for me in the past (Hornady 55 grn V-Max) and finally found what that barrel liked. Great groups with several different powders and loads. All were one notch back from maximum, hot but not what I would think of as pushing the edge of the envelope.
My guess is that the 1 in 14 inch twist barrels must do best with the 40 grain bullets. My optimistic hopes of using the 40 grain bullets in my 1 in 12" barrel to approach 22 Hornet performance were dashed by 3" groups at 50 yards with the light charge/light bullet loads.
I am happy to report though that the 55 grain bullets did pretty well at 2,000 fps velocity. - A good thing as I have two pounds of AA5744 en route that I ordered last month. At 12 grains per load, that ought to last me for a while with those mouse loads.
In this case at least, it looks like bullet weight was more of a factor than the powder used, or the velocity I tried for.
Best results with the 55 grain V-Max in this gun came with W 748, H-4895 and Ram-Shot Exterminator. None of these three stood out as being noticeably better than the other two, at least not so far... The Exterminator powder is something new to me, it is a ball powder that is fine-grained, easy to measure and goes everywhere if you happen to spill a little bit of it.