I have calculated the state of stress in the Bat Machine Co. Inc. 8.5" action for the .408 CheyTac Cartridge with a 0.630" case head diameter. The calculation was done with the LSDYNA FEA code. Two conditions were calculated. The Nominal condition is for a 60,000 psi pressure (hot load) and an intact cartridge case with an internal diameter of 0.540". The second calculation assumes the worst case of a ruptured cartridge case head (but still contained within the chamber) with 60,000 psi pressure over the full diameter of the 0.630" case head. The high strain rate that occurs when a cartridge is fired was not considered. Typically, steels have up to 10% higher yield strengths at higher strain rates and that extra strength was not included in these calculations since the high strain rate properties of these steels was not known.
Summary Table
Maximum Effective
Stress at the bolt lugs (psi) 
Maximum Effective
Plastic Strain at the bolt lugs (in/in) 
Maximum Effective
Stress on the action (psi) 
Bolt Face Axial
Deflection (in) 
Action Axial
Deflection (in) 

Nominal Condition Intact Cartridge  181,500  0.0020  119,900  0.0070  0.0020 
Ruptured Case Head  185,400  0.0046  163,300  0.0095  0.0028 
Nominal Condition 60,000 psi with intact cartridge.






The worst case condition with a ruptured cartridge case head and 60,000 psi pressure over the full diameter of the of 0.630 diameter" case head.





Another view of the bolt and the effective stress. 
The same view as above with the bolt lug removed and showing the fringes of Maximum Shear Stress. Yielding in shear would occur when the shear stress exceeds ~1/2 of the yield stress or 90,000 psi. The Maximum Shear Stress (the red fringe area) at the bolt to lug junction is only 55,300 psi at it highest point or 61% of the yield shear stress even for the worst case loading. 
Material Properties used in the calculation:
Rifle Bolt of 4140 steel heat treated to a hardness of 4345 Rc
Rifle Action of 174Ph Stainless Steel 3638 Rc
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