28" has been the accepted avg back to brisket demension for a mature 6x6 Rocky for decades. This is not to say that some don't go a couple inches bigger or smaller, but 28 is the accepted avg. This is also why the subtension of a Leupold Fine Duplex reticle is ~56moa. (or 28" at 500yds on 10x and 1000yds on 20x) Old man Leupold knew exactly what he was doing when he designed the Leupold Duplex Reticle all those years ago. For the express purpose of ranging Rocky Mt Elk.
Bracket elk back/brisket (post to post), divide mag power by 2 and that is how many hundreds of yards it is away.
Hunt'nFish