So now I am rethinking whether an aftermarket barrel is a bad idea in working up a load. I would assume the test barrel provides a fully supported chamber, so brass deformation would never really be anything they would see. I think it would just make it more difficult, and could hide a lot of the early pressure signs.
I do watch my primers as well. They seem more difficult to read though. There are degrees of flattening, and I cannot find any true measure of how much flattening is the upper limit. Maybe my stock G20 Gen 3 barrel is a good choice after all. I can certainly read bulged brass better than flattened primers.