It's going to prove quite difficult to get a 400 Legend to feed reliably from a high capacity double stack magazine.
Been there, done that. 20 years ago.
Tony Rumore
Tromix
No one here has had more experience with mags than Tony.
A solution to no problem and as has been stated will mostly just cut from the 350 sales, so no idea what Winny was thinking.
Also, having tested a lot of bullets for my former employer, especially 10/40 back in the day, I don’t even think 10mm monometal bullets will take those impact velocities at closer ranges.
I have been playing around with the Wilson 300 hamr and have to say it is the perfect deer/pig ar caliber to me for 250 and in. The 130 Speer hot cor does a number on them, feeds well and is light on the shoulder.