Other hard to ignite propellants are used almost entirely for full-throttle magnum revolvers, so it's moot to discuss if magnum primers would be needed in semi-auto cartridges.
Moot? not if you're someone like me who has full throttle magnum semi auto cartridges.
And, for them using W296 I do use large pistol magnum primers. I also use magnum primers with 2400, though I do no NEED to.