PGW makes a very good point. Torque applied to standard threads creates both axial and radial forces at the thread interface. Buttress and square create principally axial forces. This is quite desirable in certain applications. It should be desirable in rifle barrel threads as torque applied does not create a hoop stress in the receiver. BTW - square threads have been used in rifle barrels over 100 years ago with the Ross. (made in Canada
)
However, for a given applied torque and thread pitch, square threads will create much more axial force than standard threads. My estimate is about 35%. Accordingly, to get the same seating force at barrel shoulder,
less torque is needed using square threads. This is why it seems incredible that someone would spec 500 ft-lbs of torque on a Remington action using buttress threads - that would amount to the axial equivalent of 675 ft-lbs of torque applied to conventional threads.
