which rifle backpack do you use?

Eberlestock J107. Very well built pack, excellent harness, lots of storage options, and room for two water bladders. The rifle sleeve is very handy and can be easily accessed without struggling.
I shot a goat last year and had over a hundred pounds in my pack and climbed down about 2000' of vertical (including a 200' vertical wall) and then about 2 miles of very rough terrain without even getting tired shoulders...my legs on the other hand...my pack was drug on several rock outcrops and I went for one short slide, and it shrugged off the rocks very well.
I have used an Eberlestock Gunslinger the last 4-5 years. The second trip after packing a rifle for 10 hours for 3 days I put a Kifaru Gunbearer on the Gunslinger. Since that time I have only used the scabbard on the pack a couple of times. If you're a serius packer I'd take a look at the Kifaru and you can put it on any pack of your choice.
I have a J104, and like it alot. However, I would like to see a smaller dayback version, along the lines of Eberlee's mini me model, but with a waistband to help support the weight of the rifle. Maybe, I need to look closer at the gunslinger.
I was just looking at some photos of the Gunslinger and I wondered if
I would be able to glass without taking the rifle off.
What about a Badlands pack? They have different sizes depending on what you are looking for and are designed to hold a rifle. I was checking them out at Cabelas last weekend and am debating between that and the Black Creek.
I have the blacks creek rigg-itt with a kifaru gun bearer.
It's light.
It's adjustable.
It can be modularized in anyway for different hunts. (Not just blacks creek stuff)

And I can haul out game with it.

Take a look at it, it might serve your needs.