RE: hand wrench and sledge hammer

>torquing is more of an art than science.
Too true
The NASA Fastener Manual shows preload accuracies as follows

'Feel' ±35%
Torque wrench ±25%
Turn of the nut ±15%
Load indicating washers ±10%
Fastener elongation ±3-5%

Turn of the nut and load indicating washers are accurate but only for 'standard' installations, like buildings or machinery. With soft gaskets you don't know for sure how many turns provide the right preload, so you're back to 'feel.' Probably good fitters with specific experience in a given installation can do better than 35%. If it were me I'd be inclined to figure out what torque I needed then discuss it with the best fitter I could find and adjust accordingly.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw@skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)