A rule of thumb is that single-lug bolts not be loaded for chamber pressures above 40,000 psi. Modern bolts are commonly loaded to 55,000 psi and even more. Safety testing is generally 50% or more above this.
Measure the base area of the bolt lugs in square inches. That lets you calculate the shear force on the lugs in psi. Odds are it's beaucoup less than the yield strength of the steel.
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