Ruger improved the accuracy of their large-frame single actions in 2007. They did a new cylinder making process that reams all the chambers with the same bit/reamer tools, leading to uniform chambers instead of the prior pattern of mis-matches when they did an all-six-at-once setup with six different reamers going at once.
You can ID these improved guns (on the large-frame series!) by looking for the "lawyer's warning billboard" on the barrel. If it's on the side, it's the older setup. Newer, it's under the barrel.
This does NOT apply to the New Model "mid-frame" series that first came out in 2004 with the New Vaquero. It's also on the 44Spls (all), the 50th Anniversary 357 Blackhawk "Flattop" specials of 2005 and a few of the new Blackhawk Flattops in 45LC/45ACP convertible. All of these "mid-frames" have the improved cylinder and have from the beginning (2004). When I was shopping in 2005 I went with the New Vaquero because it had that process done when the large-frames didn't yet have it...my gun is very, very accuracy (and is even a bit moreso now that it's been converted to 9mmPara with a true .355 Douglas Premium barrel grafted in