
I never did remove all the lead from the throat. In addition to the Birchwood Casey lead removal cloth, I tried JB paste, and fine steel wool wrapped around a brass brush. In the end only about half of the lead was removed from the throat.

Then I fired 5 firelapping rounds with #500 grit. The idea was to knock off any microscopic burrs in the throat -- the rest of the barrel does not need to be lapped. That brings the total firelapping rounds for this barrel up to 25 (10 #280 and 15 #500).
The original batch of cases was set aside because the necks had been turned too close to the shoulder and they were prone to separating at the neck/shoulder junction. A new batch was made and this time I turned the necks a little thinner, aiming for 0.0105". Loaded necks ran around 0.331" in the 0.332" chamber.
Now continuing the search for Mr. Happy Powder ...
I meant to use magnum primers with Accurate 2520, but unintentionally loaded it with Federal #210 standard primers. The ES was pretty lousy so apparently AC2520 does prefer a magnum primer, plus it would probably do better at higher pressures.
I'm finding that this chamber gives velocities about 100 fps faster than Quickload predicts, hence most of these experimental loads are faster than the 2300 fps goal.
As you can see, IMR3031 made a shotgun pattern. N135 was the only powder that even tried to group today.

Showing the "problem" land at the entrance to the throat, taken with a Lyman borecam. As you can see there was still lead in that spot at the beginning of the test, and the amount of lead stayed about the same. Next time I may try shooting a few jacket bullets to knock the lead out, since I have already tried everything else.

All of today's powders left some carbon, and some lead in the corners of the grooves, particularly in the middle of the barrel.

Well, this chamber & barrel combo continues to be a dog. I have lots of questions but not many answers. There are 2 more powders to try before I give up.
