Old thread but I thought I could add some reality to it. The story behind the RSM and Express lines, and I believe some others such as the Red Label and Gold Label shotguns.... Is that old Bill Ruger had always wanted to make some higher quality guns but being a good business man he listened to the bean counters and built his business on decent quality at a good price and supplied products that most people could afford. He did well and enjoyed the fruits of his labors aboard his own personal Yacht.
however like many in his position, he eventually decided he was wealthy enough that he was damned well going to do what he wanted to and thus began the period of the best products ever built by Ruger. It is said that every RSM and Express rifle went out the door with hundred dollar bills stuffed down the barrel

Figuratively, not literally.

In other words, the company was selling them for less than it cost to build them. Even today, they are way under priced for what they are on the used market.
Furthermore, the machinery that was used to build the Magnum Actions was worn out. There is a PH in Africa who was telling me the story about a 416 Rigby RSM. I don't remember all the details but I think the story was that a dealer or distributor in South Africa really wanted more of the Magnum rifles after the announcement that they had been discontinued, obviously because of a real need over there. Ruger agreed to make one more short run for him. As he sold out of those, one or maybe it was three of them had some major problems. Ruger's Customer Service Department was contacted and true to form, they agreed to stand behind the rifles and built I think it was 3 more. But explaining that that was it! They were taking the machinery out and scrapping it. I'm guessing those last rifles needed some level of hand finishing.
So Ruger no longer has the equipment to build a true magnum length bolt action. Their answer was to work with Hornady to develop the 375 Ruger caliber which can be fitted into a 30-06 or 300 Win Mag length action. and then necked it out to 416 Ruger.
This is also why we will likely never see a Ruger African in 300 H&H Magnum. They simply do not have the machinery to build it.....