Hi rory,
I've read that and tried it. It sounds great in theory, but doesn't work to well in application. Didn't use a pop can, I used shim stock. If you use a mic and roll the slug to hit the high points you can get very close, not perfect, but close enough to know if there is a problem.
I've seen lots of 1 moa from cast shooters using Lyman's .311299 or bigger,
Haven't seen any signed targets from jacketed rounds, not to say there not out there, just haven't seen them.
The ever elusive 1 moa was unheard of in 1917 for an issued infantry rifle. I think the specs were closer to 4 moa. When the tin coated bullet came out they tighter up, set alot of new records and actually redesigned The targets to increase difficulty to reflect the improvements.
If anyone has a 5 groove eddystone that's shooting 1 moa that's awesome, pm me and let me know what the secret is! I'm still trying to get there with mine.