I recently bought a 99-E in .300 Savage with the aluminum rotor.
It feeds and chambers both the Federal 180-grain and the Remington 150-grain factory loads with no issues.
I've shot several boxes of Federal's 180-grain load in several .300 Savages, lever, pump, and bolt, with never a problem.
Bottom line, I don't think it's the ammo, unless the bullets are seated out to a longer-than-normal COAL.
