What's your rule of thumb for changing COAL?

[Dougfirtree]

When you're working with load data that has a different COAL than you'd like to use, what's your rule of thumb for adjusting where you start with powder charges (or where max is apt to be)? In other words, if the load data is based on a 2.73" COAL and you'd like to use 2.8", how do you alter the powder charge for start/max loads? I feel like I'm generally able to look at different sources and make an educated guess about a safe place to start, but I'm wondering if you have a more concrete formula, etc?

 

[grizzly63]

Don't make it harder than it has to be. Start 10% below max and move up until you are happy with accuracy or you hit pressure signs. Make sure your mag and chamber will accept 2.8 first.