Okay, I guess this is a kind of physics question.....

[ABNAK]

Does having a LH threaded muzzle device on a RH rifled barrel keep it from loosening (or vice versa)? i.e. is it beneficial to have the muzzle device threaded the opposite direction as the rifling inside the barrel?

[jsbhike]

I haven't tested it myself, but unthreading is allegedly the reason most FAL variants switched from RH to LH muzzle devices.

The hump on this FH opposite the bayonet lug is for a key that locks the FH to the barrel to prevent movement which is the case with most RH thread FAL's, but as far as I know is not a feature on the LH thread models.

https://www.apexgunparts.com/t48-fal-type-flash-hider.html

[FromMyColdDeadHand]

Only north if the equator…

[Inkslinger]

I can’t imagine how the directions of the rifling and the MD could have any interaction. These parts are not rotating during operation.

[ABNAK]

I can’t imagine how the directions of the rifling and the MD could have any interaction. These parts are not rotating during operation.

Inertia? Gases exiting the muzzle?

[utahjeepr]

This is actually a thing, but the forces are easily overcome with applied torque of the muzzle device.

Older Chrysler cars used to have RH and LH threads on the lugnut studs for each side of the car for similar reason. The increased use of pneumatic impact guns, and the resulting increase in snapped studs put an end to that. Combined with the added cost to manufacture, of course.

Bottom line. People have developed a preference for RH threads. It's easier to adapt physics to people (apply torque/threadlocker) than to adapt people to physics (LH threads).

[Inkslinger]

Inertia? Gases exiting the muzzle?
Those forces are being directed out the barrel not in the direction of the threads. I mean, maybe if the MD was only hand tight it could probably happen just from the harmonic movement through the barrel. I’m am far from a physicist though…