Follow what wind Gypsy said above to figure out if the brass fits the new rifle.
I would load some at a medium charge and use those for break in and sighting in. Then start your load development.
I do like to break in barrels and I think a lot of the info on not breaking in is from non factory barrel guys.
I’ve personally watched every barrel get progressively easier to clean.
I start by cleaning all the factory gunk out, it takes a long time.
Shoot once, this is normally my bore sight shot. Clean it until patches come out like they went it, again this will take a long time.
Next I’ll shoot 2-3 and usually be pretty close to hitting point of aim. Clean it 100% again. This time it will take a few less patches than before but still require effort. Repeat shooting 2-3 again and clean, should be easier but still not that fast to clean, shoot another 2-3 etc.
typically about the 10-12 round fired mark when you clean it will still take less patches than previous but you will notice after the first few patches the fouling is basically gone.
That to me says the barrel is smoothing out and whatever was hanging onto the fouling isn’t doing it anymore.
Shoot a 10 round group with your moderate load and see if you are happy that should tell you if you need to change a component in about 20 shots. You will have a good idea what the groups are like but cleaning each time will affect those some.