Winchester has come out with a new straight walled cartridge to market to the straight walled states.
I believe it's a .223 blown out to .35.
Should work in AR platforms. And I believe Winchester is releasing their XPR rifle in it as well.
Here's a link for some info
https://www.shootingillustrated.com/articles/2019/1/22/first-look-winchester-350-legend-cartridge/
I'll stick with my .375 Winchester and .45-70s currently. But it's always fun when something new hits the shelves.
-Jake