Gary, it is very interesting what you say about barrel twist. My rifle was built by Darrell Holland, using a Hart barrel hooked up to a blueprinted Remington 40X action I purchased in 1996 from Walt Berger's brother. The stock is from McMillan in northern Phoenix. I had the parts shipped to Holland, who then put everything together. It was my original idea to use the rifle for both ground squirrels and coyotes. It became fairly readily apparent that the rifle was too much for ground squirrels, but fine for animals the size of badgers, rock chucks, coyotes, and such.
The rifle is a single-shot, but it has made me concentrate on getting my ranges correct, knowing what wind adjustments to make, and generally staying focussed on not missing shots, not being seen, smelled, and so forth. Having been brought up as a bench-rest shooter, I guess I just don't know any other way, although an AR-15 setup is intriguing. Unfortunately, those types of "assault rifles" are not legal in my home state of California.....or at least I don't know how to get around the law. I could purchase one in Arizona, but I am so used to using what I have now that it might be money wasted.
I'll check to see what the twist is. If it is 1:12, I could choose some of the bullets you have suggested. I had loaded 1,000 rounds, using 33 grains of H4895 to push the 55-grain Noslers. As I mentioned, I didn't know better, being a new reloader at the time. There has been minimal chamber erosion, and the accuracy is almost as good as when the gun was new. When using it for ground squirrels, I was always aware of excessive barrel heat and cleaned the barrel every 20 shots, so maybe that had something to do with accuracy retention. Of course, the Hart barrel had something to do with it in my opinion.
Barry