A couple of years ago, Winchester introduced the 350 Legend, a straight wall case designed to meet the rules some states have about what cartridges can be used to hunt deer. And of course, it is suitable for the basic AR platform. This was touted as being very "innovative" but right away I thought that Winchester simply "magnumized" their old 351 WSL round, which was used in their Model 1907 self loading rifle. The new round - with a longer case loaded to higher pressures - is otherwise similar to the old round, give or take a few thousandths of an inch here and there.
As soon as I read the announcement of the 350 Legend, I found myself thinking "When is Winchester going to be INNOVATIVE and magnumize their old 401 WSL round, introduced in their Model 1910 rifle?"
Now we know.
https://winchester.com/Products/Ammunition/400-Legend