I wanted to do the backpack strap "thing" since it carries the weight absolutely best of all but I have not found a way to do it without the gun flopping around. More or less gave up on it. For a while I carried 4" barreled DA and 4-5/8" barreled SA Ruger revolvers in Uncle Mikes vertical shoulder holsters. This worked very well under a jacket if I cinched the pack belt down so the holster somewhat rode on top of the belt inside my jacket instead of bearing the weight all on my shoulder. The pack strap would more or less keep the unbuttoned jacket closed enough to conceal but I could easily access and draw my gun .. often times with my left hand with a sort of "turn it around on the way out" draw. (It helps to be fairly ambidextrous.)
Sometimes I carry my revolver in a hip holster underneath my pack strap. Depends on the gun, depends on the holster, depends on the pack. With an old Cabela's alaska guide pack frame I found it pretty comfortable. Seemed to have a "pocket" kinda behind my hip bone. Putting the gun in there didn't create any pressure points. Other packs, not so good. Generally today I choose a day pack with a flat nylon waist band rather than a padded waist band or one with no waist band at all. Most of those ride either above or below my holster positioned on my pants belt so a hip holster works fine.
Most of the time, though, I carry in either a leather or nylon bandolier style holster. I have a couple of El Paso Saddlery 1942 tankerman holsters, one for 4-5/8" ruger single actions, one for 4" S&W N frames. I did 5-6 years with those. Today, though, mostly I've switched to Diamond D holsters. I have a Guide's Choice for a Ruger bisley .454 and a Denali nylon holster which fits both 4-5" DA revolvers and 4-5/8" DA revolvers. It's the nylon holster that sees the most backpacking use along with a S&W 329PD.
All of them get a bit heavy on the shoulder by the end of the day. The pack strap option starts to look mighty good again around 2-3 in the afternoon.
There is one other option I've done. Back in times before I had good holsters I carried either an 8-3/4" barreled N frame .357 (this gun was from before they were shortened to 8-3/8" or designated as the model 27) or a 7-1/2" barreled super blackhawk in the top of my external frame pack with the right hand side not cinched clear tight, just the weight of my sleeping bag keeping everything snug but accessible. I could reach up behind my head to draw. It was pretty effective back when I was younger and more flexible.
