I'm looking for some insight on how some of you might carry your long range precision rifles for a long trek, and what equipment you use to facilitate that carry. If you care to share some pics that would be great. Mainly i'm looking to find a way to carry my rifle while wearing a ruck sack, hands free, and the rifle is decently quickly accessible. Which fancy pack attachment do you use if any?
The OP said long trek, wearing a rucksack, hands free, and quickly accessible ... that nixes some of the offerings here.
Best source of info for this will be hardcore long-distance backcountry hunters; take a look over at Rokslide if you haven't been there before.
As far as packs go, Eberlestock and Kuiu packs are okay for light-med loads, but not so great for heavy. They've also had some notable blow-outs. Eberlestock also got a little litigious when other companies started making in-pack sleeves/scabbards ... better than they did. Meh.
Kifaru International, Stone Glacier, and Mystery Ranch have been the three tier one options for a while (although MR has now moved much of of their production offshore).
I haven't seen the latest verdict on Seek Outside; Exo is generally considered the next rung down. Eberlestock and Kuiu lower still.
For a "quickly accessible" option, there's the Kifaru Gun Bearer as many have mentioned. It's a side-carry option, although the load bearing and fast deployment are good. Multiple pics here:
https://kifaru.net/store/accessories/gun-bearers/
For a more central carry option (better load distribution but less accessible), there's Kifaru's Sherman Pocket:
https://kifaru.net/store/accessories/sherman-pocket/
If you want to see a better version of Eberlestock's scabbards Kifaru's Long Range Hunter rifle scabbard might still be available secondhand:
And if you want to see an in-pack sleeve option done well, track down a Kifaru Mountain Rambler (not the Mountain Warrior) ... a great heavy-rifle, muzzle-down option. Comes up for sale on Rokslide every so often.
Video showing rifle insert/removal:
This one shows more about simulating meat carry, but Aron references using the Rambler with a 338: