I was reading some Elmer Keith this morning and read about how he and another fellow experimented with threading copper tubing and screwing it in around the primer flash hole inside the case up to about half the length of the case. He called it a duplex load. This allowed ignition of the front portion of the powder charge first. In WW II while working at an armory, Elmer reported achieving 200 fps more velocity with the 50 BMG with normal pressure. He attributed this to a longer pressure curve with more time spent at peak pressure. They also worked with smaller cartridges with similar success. I was wondering if this might have some application in the 338 Lapua and 408 CheyTac based rounds that Kirby Allen and others have developed. Looks like it could boost velocities and possibly expand the range of usable powders. Maybe they have already looked at this and rejected it, I don't know. Just thought I would bring it up, maybe old Elmer can contribute to modern ballistics even from the grave!