I'd strongly argue against this point. Most hunting rifles have 5 round mags (legal limit for hunting in a lot of places). They won't accept 30 round mags. They're also chambered in more powerful calibers which have much more recoil.
An active shooter with his dad's hunting rifle is much less dangerous than the same shooter with an AR-15 with 30 round mags.
Why not? Seems like as long as the magazine can protrude from the bottom, you can have any capacity magazine you want.
It’s not like WWII rifles had wooden furnitures as luxury items.