This thread has strayed a bit from the query about Hornady's magic. However, to chase this rabbit further into the brush ...
For the last dozen or so years there have been long-running threads on several firearms forums about the "12 Gauge from Hell". Early work was described on accuratereloading.com.
Here's a link to a pretty complete account, started in 2006 with a summary of work to that point. The thread has been updated continually with latest posts from a couple weeks ago: 12GA Rifle From Hell.
A photo from that thread. The case is formed from a 50 BMG.
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--Bob