I will post my answer to your PM here as others might also have an opinion or disagree with me.
I have 3 main packs at the moment a Lowe alipine 75-25lt( awsome ), Carrimore75lt (nice ) and a Wilderness experience 50 lt ( my wifes ) all these pack are great and the first is my main pack of choice but none can also carry my rifle easily. The M3 operator is a little smaller then the first 2 but has great storage options for me. My spotting scope will fit down the side pocket and my trpod in the other . If you dont want to use the full capacity of the bag then just tighten up the compresion strap and reduce the volume .
The ability to carry my rifle hands free is a must when in Nz because unlike many others i dont shoot my Tahr from the skid of a hovering chopper and instead choose to climb and hunt fair chase.
When climbing high and i mean climbing not walking up a steep hill you need all your gear close as posible to your back so i travel light from a fly camp and keep my compression straps tight pulling my rifle in close . When i get my animal i let out the straps load up and lower my pack down the bluffs.
As for places to get one just do a google search on it and you will find several good sellers out of the states and with our great Aussie dollar at the moment they are not all that expensive compared to Mac pac or Carrimore.