And to reiterate, I think (particularly if you are used to your army ruck) There's nothing wrong with using it for a bit - yes 7 lbs is monsterous for what we're often talking about carrying, but I would
lighten up the rest of your load first - once you notice you're carrying 20 pounds of gear in your
7 pound ruck - then it's time to think about "ok, if I'm normally carrying this.. what pack should
I buy" - it's a lot easier to buy a pack knowing what you're carrying in it, than not.

To put it another way, I typically head out for a weekend with about 18 to 20 lbs on my back,
carried in a pack that weighs about a pound and a half or a little less. However, you wouldn't
want to use my pack, unless you were that light in the first place, because my pack is not designed
to carry, and won't be comfortable with heavier loads than that. I too have the giant 7 lb ruck - a civilian style one - for big loads in the winter, hunting, etc.