I am not a fan of stretching the limits of firearms.
It’s rough on me and its rough on the firearm.
I shot an Ithaca 12 ga pump with a pistol grip and 3.5” 00 buck magnums once.
I got two rounds off, and I think i fractured my hand.
I hurt for over a month.
I agree...I was concerned about the loads so I called Winchester about the Takedown (a Carbine)....they said ANY commercially manufactured ammo (45LC - including 300 GR) is safe to shoot in it....none of the other firearms’ manufacturers recommend that same cartridge that I can see.
Oh...and about the PG shotgun....try looking into a Knoxx recoil grip...they are GREAT! Significantly reduces the recoil...