Bolt thrust is an engineering equation used to determine shear strength for locking lugs in a firearm. From the equation the type of steel can determined for construction of the lugs when you are designing a gun..

If you can determine the type of metal used for the locking lugs in an existing gun you can determine the predicted strength of the lugs.

It is often thrown out in gun build ing discussion

I am sure that bolt thrust is part of the equation into the double gun design, but by its configuration it seems other parameters are involve.

This is at the very tip top of my knowledge on the subject. At college this was touched so we were aware.
Beyond that it was implied that this was higher level of knowledge than was need for an ordinary gunsmith, being in the area of engineering.

I regret not going on and getting the 4 year degree-Manufacturing Engineer.