So, I tried out 6 different loads of .223/5.56 last weekend. They were 3.2 gr and 3.3 gr of Titegroup, and 8.0, 9.0 and 10.0 grains of IMR4227 along with some heavy loads of 26.6 gr of Ramshot Tac all under Western Metal 55 gr FMJBT bullets.
The Titegroup rounds were very quiet and didn't sound like they were supersonic but no chrono to be sure. The IMR loads were taken from the data for .22 Hornet and were still very mild with hardly any recoil. At the same point of aim they landed about an inch higher than the Titegroup loads at 25m. The TAC loads were loud and fast and landed just slightly higher still. Even the 10.0 gr 4227 loads wouldn't cycle an AR though but worked just fine in a bolt gun. No significant difference in the horizontal plane between any of them. Pretty much textbook vertical changes only. That was interesting. Will definitely be loading up some more 4227 lrounds.