As a general rule, mine seems to like the flat based bullets better than the boat tail bullets. I don't know if the Nosler 40 grainers are a boat tail design, but I know that the 55 grain pills are.
I have been shooting mostly 40 and 50 grain V Max bullets out of my Ultra. I know it will shoot the 50 grainers good, and it seems to like the 40 grainers equally, but I haven't shot them as much as the 50's.
You might try the V Max bullets. They seem to shoot as good as the Nosler products, and they're cheaper. They seem to come apart better too.