Bolt thrust (no friction) is frequently calculated on the inside diameter of the case at the web (since this is the only portion of the base 'touched' by internal pressure). For the .223 Rem. with an OD of .378" and walls .020" thick, we have an ID about .338", radius .169", area .0897". At the proof pressure cited, this would give 6990 lbs. of thrust (remember, no friction). That's as close as I can get to Ed's numbers using the old πr² business. Much depends on what one considers to be the effective thrust area - and there appears to be considerable disagreement, with some using the OD and others the ID at different points.
I picked the biggest dimension and still did not get Ed's numbers. Maybe the source of his spread sheet found a way of creating energy. More pounds of thrust out than pounds of thrust in. Would'nt Newton be surprised?

I still don't have an answer of what % breech friction to use in designing the next generation of thundersticks.