I backpacked a couple of times with my 629 Classic 6.5". The weight wasn't really the problem for me -- I was carrying 35 lbs of stuff on my back anyway -- but rather the holster location (under and just below my backpack hip belt) started to rub a hole in my thigh.

I've since wised up and carry my 629 Trail Boss "tanker style" across my chest.

--Neill