Not really. To figure the strength of a bolt you multiply the width of the lugs by the length behind the recess of the bolt face (x). Then draw an angle from the recess at each side of the lug to the top middle front of the bolt between the lugs. Measure the thickness of the web between the lugs and multiply that by the length of the 2 angles(Y). add X and Y together and multiply the yield strength of the material (apx 160,000 psi) for 158 and 9310. Then multiply that by 7 for the number of lugs.
Then to figure the trust of the cartridge figure the area in the diameter of the rim and multiply that by the PSI at maximum pressure.
The Grendel has much more area so the thrust will be much higher. That and the fact the web is thinner between the lugs makes the Grendel bolts much weaker than a 5.56 bolt.
In the firearm industry there should be a 2:1 safety factor engineered into every part. Meaning it should be twice as strong as the maximum pressure used. The Grendel and 7.62x39 barely have a 1:1 ratio.
Now, now the first half of this post is legit.
It's one thing to be able to work out a problem, it's an entirely other thing to understand that problem.
The dimensions of the bolt are critical, but only part of the equation here. You've got the bolt's strength, hardness, and the force being placed on the bolt.
The 5.56 NATO is a max 60ksi round, while the SAAMI Spec Grendel is a max 52ksi round. This results in a significant difference in your force on the bolt.
Your assumption of a FoS (Factor of Safety) of 2 for the 5.56 bolts is incorrect. The 5.56 NATO like the Grendel, 458 SOCOM, BEOWOLF, etc... were developed for a platform that wasn't initially designed for such higher powered rounds. The AR15 was initially designed for a .22 caliber round operating at roughly 50ksi. But I digress....
The bolts for all of these rounds achieve a FoS of 1, which has proven to be sufficient when supplemented with properly selected high quality materials and proper manufacturing processes.
9310 and Carpenter steel are both high quality, strong materials that are made stronger through heat treating. (see increasing yield strength) However, the metals can be heat treated to a increased strength where they become hard and brittle. This will make the material more susceptible to stress fractures from the impact of the rounds thrust. Stress fractures are your bolts worse nightmare. A small stress fracture will spread at an exponential rate. The 90 degree edges of the bolt lugs make the lugs the most susceptible area of the bolt. As you understand this, you begin to understand heat treating to be the art that it is.
Now let's look at the Grendel(actually originally the Beowolf) Bolt again from a true overall viewpoint. The Grendel was always intended for the AR15 platform, thus all the factors we've discussed above were balanced to fit within the parameters of the AR15. When you understand all of this you begin to understand the fine engineering job that is the final Grendel Bolt.
The Grendel Bolt design was proofed at 60+ksi. Per the design the Grendel can be fired at the pressures of the 5.56 NATO, as some people do. This is where you've seen bolts break as the Grendel Bolt won't sustain continuous operations at 55+ksi. Eventually material fatigue sets in and you get stress fractures.
