I was able to handle the round at the SHOT Show in the Winchester booth. Savage is going to make the first rifles chambered in it, and they have a reputation for accurate barrels.
It's based on the beefed up case from the Winchester .27 caliber nail set blank. The case is heavy, as it should be for the velocity they're getting. Winchester spent 3 years getting this round perfected, and the tests show velocities just over the publish velocity.
It's almost big enough for a center fire primer, but not quite, which is why it's a rimfire round.
Hope this helps.