Welcome to the forum Hussey500.
What part of Texas are you from? Who is building your rifle?
As you are aware of the main problem in building and regulating a double is once you decide on a load and regulate your rifle with that load, that is pretty much it. You can’t just change the sights to get it to shoot a different load or bullet weight.
I would recommend a 180 grain load as being best for what you said you intended to use it fore.
Are you going to scope it?
Bill