That an action wrench is defined as rear entry, does not imply where
it applies its force to an action. Some will apply force to the entire length
of the action and some only to the front reciever ring. I have seen some
poorly designed wrenches that are only half as long as they should be,
thereby requiring the action to flex. To damage an action, you only need
to exceed its elastic limits torsionally. How much this amounts to, I don't
know, but no doub't many things come into play. I would prefer to apply
the force as close to the threads and shoulder as possible, allowing the action
to receive no torsional stress. The T handled wrenches as sold by kelbly's
do this correctly. It also allows two hands for a balanced force. Given a barrel
well fitted and installed at 80-100 ft lbs, may require 100-140 to remove.