223, although it seems like a pretty simple and straightforward cartridge to load for, does have it's idiosyncrasies.
After a few issues I began to use a CCI 450 Primer, at least until I had determined my load. Especially important with starting loads, and with ball powders. I don't think the powder itself is the issue, it's the fact that the balls inhibit the primer flame or something like that, just my WAG. After I'd reached the velocity i wanted, or the pressure was nearing max, then i'd test other primers.
I put my 223 away at the request of the government, so I'm going from memory, but IIRC, the CCI 450 is the only real Magnum primer for small rifle. The 7 1/2 Rem is a harder or thicker cupped version of their regular primer.
I did buy a brick of Federal AR Match primers but testing has been on hold for over a year.
My H335 load was with a 50 gr bullet and 27.3 grains, but with the 450 primer.
I did seem to favor BLC-2 and CFE 223 later on, not sure why I abandoned H335.
I like the 223, and once you have a decent load, it's a joy to load. It is one of those calibers that weighing charges, cleaning primer pockets, trimming cases and that sort of stuff doesn't seem to matter much. However, I did do extensive case prep initially. Weight sort, flash hole uniform, trim and deburr with a Lyman VLD (22º) tool. After that, just load. I also avoid top loads, the 223 seems to be at home with a middle of the chart load.
I got a bit annoyed with paying up for bullets, so settled on Hornady bulk, 55 gr WC. With 26 gr of CFE 223, a Rem 7 1/2 gave me a bit better group in a cheap prohib.
