Glockster, do you still have cases from the Gibbs?
An all too common problem when changing an existing chamber is that the next chamber is cut out of line. The reamer has nothing to line up on except the orig chamber. Any movement/chatter/misalignment and the new chamber is cut out of true.
It takes a lot more work for the smith to set up the reamer and bore properly. Plus since this was a factory barrel, the chamber/bore might not have been true with the outside of the barrel. If the chamber was indexed using the outside of the barrel, you got a wonky chamber for sure.
This chamber will never shoot well. You can check for runout of the fired brass. If this is oval or bent, then that is a definite sign. However, the chamber might be true but not line up with the bore so the fired case is fine but any loaded cartridge would be offline when a bullet was sent down the pipe.
You can quiz Guntech. He does a very good job and knows how to line things up.
The next one is the throat. If the chamber had a longer then desired throat, it would never shoot well either.
After playing with many cartridges of all sorts, I can conclude there is no such thing as an inaccurate cartridge (within its intended application). In fact, many bottle neck cartridges I thought poor shooters ended being spectacular.
The key is in the intial chamber cutting and barrel install. Any oops here and doesn't matter if you have 6BR or PPC with a Kreiger barrel spun onto a Stolle/Panda action, wonky chambers don't shoot.
Jerry