Thankfully that isn't the only 1000 yard range in LA anymore. The Fusilier Complex in Arnaudville opened their 1k range earlier this year. Roaming Shot in Slaughter is new as well.
I would tend to think the 5" group is the shooter and not the load, especially after shooting many rounds of a magnum. (I'm not trying to say anything about your skill. That **** is hard on your body.)
I do want to be clear about the "ladder" though. I'm not looking for nodes, flat spots...
You shot 27 rounds in 9 three shot groups, across different charges. There isn't anything statistically significant that can be drawn from such a low number of shots. You're not going to shoot a deer for groups anyway, so why does it matter if it's a half inch or inch and a half group?
You...
Do you like beating yourself up with recoil? Do you like wasting components and barrel life? I sure don't.
You're not shooting enough groups to have any statistical significance of a "node" (they don't exist), so why bother?
Purchase quality components. Use a powder with an appropriate...