RE: most accurate single shot?
Since you ask about single shots I will limit my response to those. I have had many single shot rifles. The Browning is very accurate. I had one in 220 swift. It shot groups well under one inch with only minimum tinkering. I have had several No. one Rurers and a couple no 3,s. They all shot very well. One was in 416 Rem mag, I only shot 3 shot groups for reason of pain and agony but the gun shot well. All of the H&Rs I have had shot pretty well like 1 1/2 inches or better. However if you can believe it the most accurate one I ever shot was the rifle barrel on one of those Savage 30-30 over 20 guage shotgun. I shot groups with all bullets touching many times using nosler ballistic tip 150 grain bullets. One calm day when everything was clicking right, I shot a one inch group with it at 200 yards. I did have one 270 Remongton pump that shot just as well as that Savage.