Pressure tested data happens in SAAMI min spec equipment, you have loser tolerances in a production rifle; so more gas bleed-off. When you match/pass book velocity, regardless of powder charge, you have gone over-pressure.
This is not necessarily so. I have a standard 223 that exceeds Hodgdons book max speed at under max charge. It also exceeds Noslers max speed for a given charge under max and have had no problems at all.
I don't think so. Forget the chronograph. It's only an indirect measure of pressure and a bit crude at that. There was a gun purveyor who had 10 "identical" rifles in which he shot the same load. Velocities between the rifles varied by as much as 200 fps.
Pressure signs are going to vary depending on the cartridge and the gun. With a 223 cartridge, there probably isn't going to be much primer flattening or even sticky extraction in a bolt gun. What will probably happen first is a primer leak or a pierced primer.
What I've found useful, if you're shooting an accurate gun that is, is to look at group size. As you start low and work up, groups will generally get smaller up to a point and will then start to open up again; sometimes with a marked POI shift. I stop where the groups are the smallest.
Again the highlighted is not completely true.
Shoot your groups for accuracy over a chrono.
I have had stiff bolt lift, hard extraction, and no primer leak or pierced primers from a max load of 335 and 8208 when the load was developed in cooler weather and then shot on a much warmer day. I have found 335 to be very undependable @ max load above 90 degrees. Plus its extremely dirty.
OP the 223 Ackley should give a case capacity gain of 2.2 to 2.8 grains H2O over the standard 223.
So I would work up and watch the chrono and group size, groups may get smaller but could get larger. Its also possible that you have reached a plateau where adding more powder will not gain you any significant increase in velocity. As others have said you may have to go to a different powder/primer combo to get what you are seeking.
