Ultralight hunting = <20lbs.
Read the following to see how I came to this conclusion, and let me know if I'm about right, or way off base.
Personally, this is how I would look at it:
Create a packing list as if you were just going backpacking. (i.e. appropriate UL gear for the terrain, weather, etc. that the hunt will take place in) ~ <10lbs.
Then, just as you do for your UL backpacking, go over your hunting equipment and decide what you Absolutely MUST have, and what you can do without. For example:
* Substitute the pack in your UL list with an external that can comfortably carry your max load after you've harvested your game.
* Do you really NEED 50 rounds of ammo if you only have one elk/deer/sheep tag? I would take maybe 5.
* Change wood stocks to synthetic.
* Do you really need all those knives? Or can you get away with just a Mora and a folding fiskars saw and finish your work at camp/home/town.
* If possible/desirable, take up traditional bow-hunting with a recurve. (not a compound, weighs just as much as a rifle...)
What else do you need? Everything other than your weapon/ammo and field dressing gear should already be in your UL backpacking list. The only thing you should need to substitute is your pack.
So, what's considered a lightweight production rifle nowadays? 5-6lbs?
Here is my proposed UL hunting weight formula:
(UL gear list - backpack weight) + new backpack + weapon/ammo + Field dressing tools.
So using the above for a rifle hunting trip, using a scope would look something like this(weights approximate, substitute your own actual weights):
Weights in pounds: (8-1)+3+7+.7= ~18lbs.
In short I would say, if you are rifle hunting, under 20 lbs. would be considered ultra light hunting?