Sounds like it needs a little more break in, I would repeat the brake in process and see if it improves. (Some barrels need more brake in than others).
It is not unusual for this to happen after 6 or 7 shots until it is broke in well.
When testing loads, I clean after each 5 shot load and shoot a fouling shot to keep things consistent. That's great if it doesn't need a fouling round, but that Is also a sign that it is fouling faster than normal.
You might also try to see how many accurate shots can be made with only one bullet and then try the same test with the other bullet you want to use. I say this because I have found that some bullets foul worse than others because the copper content is greater.
J E CUSTOM