I shot the barrels out of several of the exact same rifles in the early 80's on chucks and p. dogs.
Using Win brass always, and Fed 210, the load of 38.5-38.7g of H4895 with a Sierra 85g BTHP always shot fantastic groups at 200. You will have to tweek the seating depth for what the rifle will like.
I also shot several truck loads of crows with a load of 49.0-50.0g of Win 760 with the 60g Sierra Hp right at 4000 fps. This is a great coyote load also. This load shot groups in the area of around .300-.375 in my guns.
There are a couple of powders and loads that are the mack daddy of all loads that I have ever shot in the 6 Rem. One is with a really stout load of R#19 achieving 3600 fps out of a 26" barrel with the Sierra 80g Blitz. With the extreme velocity of this load along with extreme accuracy, 400 yards is a chip shot.
Also, I shot an over max book load of IMR 4064 with the 80g Sierra at 3500 fps, Win brass with Fed 210 primers that shot with all the bullets touching at 100 yards. I clobbered a lot of coyotes with this load.
Win 760, H414, and AA2700 also produced fantastic accuracy with the 70g Nosler and Speer TNT, with all these loads achieving their their best accuracy at about 1.0g below the Max load for that particular rifle.
Hope this helps
