Hi Dan and welcome. No Sir. It will fire any standard .243 Winchester Ammunition no issue. Just match your load to the task at hand. Cheers, stay safe and enjoy! budsgunshop.com/search.php/type/ammo+%26+storage/caliber/10000606-243+winchester

It will shoot any 243 ammunition you just have to get different grains of bullet and try them to see which one the gun shoots really good best of luck

No, the Weatherby Model 307 chambered in .243 Winchester does not exclusively shoot Weatherby brand ammunition.
Here's why:
.243 Winchester is a standard caliber: The .243 Winchester is a widely used and recognized cartridge, and many different ammunition manufacturers produce ammunition for this caliber.
Weatherby chambers rifles in non-Weatherby calibers: While Weatherby does produce its own proprietary cartridges, they also chamber their rifles, including the Model 307, in various standard cartridges like the .243 Winchester, according to Athlon Outdoors.
Weatherby's accuracy guarantee: Weatherby guarantees that their Model 307 rifles will achieve sub-MOA accuracy (0.99 inches or less at 100 yards) using either Weatherby factory ammunition or "premium" ammunition, which includes many non-Weatherby brands.