When I run a test and measure extractor groove expansion and estimate the pressure with Quickload I get:
223: 74.5 ~ 86.5 kpsi
308: 73~ 78 kpsi

When you assume 65.3 ksi yield for cartridge brass and do a three dimensional von Mises calculation you get:

223: 86 ~ 92 kpsi, nom 88.8 kpsi
308 [Mauser] 77 kpsi

When I do a Lame's thick wall stress calculation with the primer pocket and extractor groove I get:

Lame's thick wall stress formula
S=P(R2^2 +R1^2)/(R2^2 - R1^2)
S = P[ OD OD + ID ID] /[OD OD - ID ID]
P [223] = .57 S
P [308] = .58 S

When I do a Lame's thick wall stress calculation with the INSIDE of the PRIMER and the RIM I get:
P [223] = ..76 S
P [308] = .7625 S

The combination of the groove, the rim, and the case head will average closer to the rim than groove numbers

The bolt face ejector slot is making a mark on the case at lower pressures than the extractor groove, so the axial stress cannot be ignored.

The highest yield strength for cartridge brass I can find is 87 ksi:
http://www.technicalmaterials.com/metal_prop/brass.html

Just looking at Lame's formula in the rim, with the highest brass strength, I get:
P [223] = .76S = .76 87k = 66 kpsi
P [308] = .7625S = 66.33 kpsi

And those numbers will only get smaller when I average with the groove and somehow add the axial stress.

I would like to believe the Lame's thick wall formula has some validity but I see cracks not on on the inside diameter in my 308 brass but radially:
picture of my 308 brass failing

How do you do a von Mises calculation?

Here are the von Mises stresses for the case head at the web and the extractor groove OD.

These calculations estimate the reduction in thrust force due to case stretching.

I have included (on the far right) a column which indicates which area, primer pocket or case web, should yield first.



ASS_CLOWN

PS - Clark, I will email the basic formula's for von Mises theory of combined stress effect.