As already said, many pistols, especially the cheaper ones, struggle to get any much past 3ft lb. Very few are close to the limit of 6ft lb, and those tend to be in the upper end of the price scale.
I use a BSA Magnum in .177, well over 30 years old and running somewhere between 3.5-4ft lb I seem to remember.
Perfectly adequate for caged squirrels (as long as you put it in the right place).
Anything bigger/tougher, I am fortunate to have one of these....................