I had chronograph the speed of the factory Weatherby ammo so I had a pretty good starting spot. I tried IMR 4831 but I couldn't get the speed without pressure signs. So I tried some RL22, that was the magic load. But with RL22 being a little bit temperature sensitive I did all my load testing in the summer with temperatures in the 80's. I could push my load a little bit faster but I am perfectly happy with where it is sitting at right now.I have found it hard to match the Weatherby factory ammo ballistics. There is not a lot of reloading data out there that duplicates the factory ammo ballistics. Your method of pulling the bullet and weighing the powder is also what I did. The problem I had when I was first reloading was I could not get the Norma MRP, so I settled on Reloader 22 and had to play around a while. At the time, RL 22 was the slowest burning powder they offered that according to the data I could find, came close to factory ballistics. Now I have just stuck with the loads I developed with RL 22. At some point in the future when I have more time I plan on playing around with some of the newer, slower burning powders.
My loads aren't as accurate as you mentioned above, but I am not sure if that is my lack of shooting ability or the ammo.
It is interesting that in the last Barnes manual that I purchased they max out the load for RL22 lower than what I am using. But I'll keep using it as long as I still have that lot of powder sitting on my shelf. But when I buy some new I'll have to drop the loading a little and bring it back up to be safe.