My reloading books indicate that Winchester 748 powder was "made" for the 223. It works well in mine. Bit dirty though. The blow back system clogs after three or four hundred rounds, which isn't long at 30-rounds a clip. I have not reloaded for accuracy, just quantity on my progressive press, and am doing fine for how I shoot. I am getting your same spread at 100 yards with 10-shots rapid fire and I don't mean steady breathing, slow squeeze, and the stuff of Bench Rest shooting. I mean squeeze and squeeze and squeeze ten times and go down range and check target. That is fantastic in my book and I am having fun. I hunt for meat and when I shoot for groups, one at a time, I use my 270 Winchester and 150 grain Hornady Spire Points. The M-16 was made for slinging lead. Yes it is accurate, but one at time? That's not having fun? Is it? Put in a 30-round clip and let her rip! That's fun, entertaining, and what she was made for. PLUS, you're getting real good accuracy there right now, depending on what you intend to do with it.