I did a similar thing to you, for coyotes, but my gun was about 16lbs.
Backpack with scabbard was the answer, I bought an Eberlestock lodrag, was great for my big rifle with big scope.
Now I have a Seek Outside Goshawk and I anchored the smaller Eberlestock scabbard to it as my rifle is an iron sighted stopper, 458 lott at just about 12lbs.
Secure, you can use a butt cover and it's essentially a gun case, for complete protection, from rain, snow, and so on, or not have it and have access to the gun if you need to draw it while on the move.
I have the rubber "backpack or normal style" sling like linked above, have had others.
Backpack with scabbard is where I'll be from now on, it just protects things right and flat works. Plus, your backpack tends to be a better and more comfortable way to distribute the weight.
Now if one is expecting to need immediate access to the firearm, like following up a wounded bear type scenario, well, there's only one answer, the rifle stays in your hands.
You don't want it slung nor in a scabbard, you want it ready to roar and in your hands.