Hammer bullets coexist with Cup/Lead Core bullet loads

Yes, I even experienced this issue using Trophy Bonded and banded solids in my big bores after using cup & core.
I had awful accuracy in 25-06 using TSX bullets in the 2000's and just brushed it off that it was the bullets because I didn't know about the phenomenon at the time. Later on I was informed and tried the 100g TTSX in my 25-05 & 257 Bee with bare metal cleaned bores and one hole groups were possible.
Same happens if you don't clean and switch back to a guilding metal jacket, accuracy is woeful.

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Barnes has been preaching this for many years. Backfire TV recently experienced this while shooting Sako monolithic bullets and cup and core bullets. He credits Ron Spomer with making him aware accuracy could be degraded going from cup and core to monolithic bullets without cleaning down to bare metal. I've shot Barnes bullets since the late 90s but never tested the idea. I just followed Barnes' advice on barrel cleaning.

Video Titled Ron Spomer Saved My Favorite Gun.
So if I understand the process, it's the composition of the copper and zinc, specifically the ratio of copper to zinc.

I am sure it's proprietary information, but I would like to know if there is a zone, this ratio to this ratio you are OK, above or below this ratio all bets are off.

Interesting information for sure and I have heard it in the past about switching from cup and core to solid copper should be avoided without a deep clean.
Dang! I guess I will be doing more of one of my least favorite things in shooting now when testing bullets and powders. I routinely clean carbon out of my barrels after every range session. Copper remediation is done but on a less frequent basis. Many people just find a load and stick with it for the life of the barrel. Maybe this is more of a push in that direction.