RG,
Have you ever replace the ball bearing by a 243 jacket seated base up in the .308 jacket ?.
As far as I understood David Corbin, there is a long long core placed (not core seated) in the .243 jacket, the .243 material is placed jacket base up in the .308 and core seated. Then a short lead core is added for the .308 point, core seat again. Then comes the final pointing.
David has customers using that set up for hunting and they seems happy with terminal ballistic and MOA accuracy (minute of antler).
He also has customers re-doing something like an A-Square Dead Tough using thick coper tubing (think it is steam grade or so). So they swag a very thick jacket, core seat and point. They get limited expansion and plenty of sectional density. That was not mentioned but I bet for a round nose.
Email send.
Oliver.