rocket420
The .223 has a rated chamber pressure of 52,000 cup or 55,000 psi.
The Lyman manual lists 25 grains of Varget as a start load at 34,700 cup and a max load of 27.8 at 51,400 cup and it is a compressed load with a 55 grain bullet. It gives two sets of load data one with a universal test barrel and receiver and a AR15 rifle.
The universal test barrel and receiver uses a copper crusher pellet and when a specific firearm is listed a strain gauge is glued to the firearm. Bottom line, the firearm or test method used effects the pressure data. When you have many manuals you look at the data and average your test loads until you find out what your firearm likes.
Any component change and firearm used can cause the pressure data to vary, as an example Winchester cases can be lighter than Remington and this can change the data.
Using your primers to read pressure signs on a .223/5.56 is guesswork at best because the various primers have different thicknesses. All my handloads are a lower pressure than the rated chamber pressure for that firearm, reloading is like playing Black Jack, stay light and beat the dealer.
Make a work up load and watch your cases and primers as the pressure increases, once the primers are not protruding and the necks are soot free your are between a mid range load and maximum. From there up in pressure you pay more attention to pressure signs and the average max load data and decide on a stopping point. The max load and the stopping point are up to you to decide by reading your cases for pressure signs and the data in the manuals. This is an educated guess because YOU do not have pressure measuring equipment. For what it is worth the majority of factory ammunition is loaded well below max rated chamber pressure and your case will last much longer when YOU are conservative in your loading.
