what are the rules about palm rests ? do they have to be attached to the rifle? can they be held in one hand with the rifle resting on them? would a dismountable fixture which was attached to the rifle by a hose clamp be legal?
i am trying to figure a way to use one palm rest for all my offhand guns without modifying them.  thanks

Hose clamp is not a bad way to figure out exactly were you want the rest.   Zip ties duct tape anything to fix it temporary.

Let me see if I can describe "ideal" or my opinion of it anyway. Draw a straight line from center of balance on the rifle to were ever you can rest the weight of the rifle. Hip bone is best,  should be a inverted Triangle, rifle down to hip up to buttplate and straight out to the rest fixing point on the rifle.

You are probably going to find it needs to swing to clear the rifles lever, so the action can open.

Boats