If you look over the attached link to Eberlestock
's website, and watch the embedded video, the Eberlestock folks will show you the proper way to adjust the pack so the weight rides on your hip where it is supposed to ride. The mid range and upper end Eberlestock packs all have adjustable yokes for the shoulder straps to adjust for your torso length and removable hip belts. In addition if you are short, or tall, or thick thru the middle (like me !) Eberlestock also sells XL and Small shoulder yokes and hip belts.
Backpack Tech Tips
The Gunrunner packs have the wider opening to allow larger rifles and optics. Good news, it is easy to put a very large weapon in the scabbard. Down side (versus packs with smaller scabbard openings) is that you have to really crank down the compression straps to keep a normal size rifle from "sloshing" around in the scabbard when you are walking quickly. I do not own a Gunrunner. However, I have no problem doing 3 mile training hikes with an 11 lb rifle and 40 pounds of ballast in a properly adjusted X1, X3, or J107 pack.
Properly adjusted, the Gunrunner will not be the limiting factor to your hunt.