I have some personal experience with these critters - we see them pretty regularly. I haven't opened them up so I'm making some inferences from experience here:
When you whack them to set the combination you put in the key and then use a metal cylinder with a slot in it that goes over the key so you can transfer force directly to the plug. It keeps you from hitting the key at all. Then you whack the ever-loving ___ out of it.
If you're not agressive enough, it doesn't work. Same force as you would apply to a 6 penny nail if you wanted to sink it in 3 hits or less. Not crazy hard, but quite a bit harder than one might hit a lock one wasn't trying to destroy.
The torque wrench that's beefy enough to compromise this shearline driectly is going to compromise the bejeezus out of the plug first.
Kodack suggested:
excessive torque on one of these locks to 'loosen' the tolerances
I would estimate that excessive amounts of binding torque would exacerbate the serrated pin condition and render the lock completely inoperable before it would alter the tolerances on the shear line. The plug and bible of these cylinders are designed to retain their integrity while the pins shear off via hammer. The pins are designed to be sheared. Intermediate force appears to just bend them around and sieze up the lock.
We sell these locks, we 'key' these locks, Master has a 100% gaurantee, and we send back a fair number that just don't work out quite right. They function sort of intermediately but they sell well so we keep them around.