Welcome to the forum. I have no experience with your rifle. So I would look at the fact that it was once an accurate rifle. With that same load, one would expect the same accuracy. So I would start looking at the parts of the rifle, the scope, the bases, the rings, and the condition of the barrel. When is the last time you removed the plastic build up in the barrel? It might look clean but there is a slight chance some fouling could be in there.

Also over the years, bullets chance, sabots change, and powders change. So sometimes you have to start over and just work up a new load.