40 ftlbs seems a bit much. I just snug them down tight, you will know when it stops. More like 15-18 ftlbs. I stake all of mine as well. If you are going to actually use a torque wrench make sure its at a 90 degree angle.
I swap buffer tubes around, so I prefer to stake instead of using any thread-locker. I do not measure the torque I apply, but I do torque them down very well. Easily more than I do my muzzle devices, which I measure meticulously at 20-25 ft-lb. 40+-2 ft-lb is correct spec.