I have worked up some .223 loads thatgave me pause. I started by doing a normal workup in a Savage 12 FVSS. The first work up came out to 28.5 grains BLC-2 and a velocity of 3300.

I neglected to write down OAL on the original workup and to be on the safe side went back and did the workup all over again. Came out the same.

A couple of people questioned the over max load. The more I thought about it the more it bothered me. Could I really go that far over max and not see any warnings and why did everything seem to be so normal and right?

Well, I started to look at the book loads and lo and behold the answer seems to be right there. The book loads max out at pressures in the 35-40 k range. I was probably loading to 50 k or so like most of my guns.

Now the question: Why wouldn't a person load to 50 k in a gun like the 12 FVSS, heavy barreled stainless? The gun could as well be chambered to 22-250. There is not all that much difference in the brass. I can certainly see not letting that ammo get into some guns, but I seen nothing even pushing the envelope with this load when you consider the gun it's for.

If you were loading for the TNT or similar very light, fragile varmint bullets the load may be low-pressure for the integrity of the bullet, not a pressure issue. Some of those style of bullet come apart in mid-air if driven too fast. Otherwise I don't know why they'd limit their data to 40,000 psi. Is it for a Trapdoor 223?

The 223 Winchester chamber has a short throat and the SAMMI pressures are a bit low; 55,000 IIRC. The 5.56 NATO chamber has a much longer throat and ammo is loaded close to 60,000 psi. The short throat is the reason why it isn't recommended to shoot 5.56 in a 223. It can up the pressure another 3000-4000 psi if the bullet jams against the lands. So as long as you don't do that (jam the bullet in the lands), you should be fine working up as high as 5.56 pressures in your Savage. It may even have a mil-spec throat these days. FWIW, I have not seen any greater strain on my commercial brass at 5.56 pressures than on my various batches of surplus brass similarly loaded.

The question I have is 35-40K WHAT? Is it PSI, CUP? UNtil you know that, the numbers are very different. CUP is NOT PSI. Hodgdon measures in CUP while Alliant measures in PSI. Hodgdon shows the same 39k-51K CUP for the 22-250 as it does for the 223.

Where are you looking?

Good point.

SAAMI MAP for the 223 is 52K CUP/55K psi piezo.

You very likely won`t see many pressure signs in primers rated for 65K psi in some cartridges, or brass that fits your chamber properly. The problem IMO will show with little warning when something decides to spike that day for no apparent reason.
Most max pressures are set to ensure a safe load in all types of chambers and tempertures. You may not be on unsafe ground in the conditions your load was worked up in, or as long as you use components of the same lot. Higher temps though, or a change from say the 65 F day that you worked your load up in to a 95 F day on the prarrie shooting P-dogs could be a problem.