The US eight-inch autoloader accepted a narrower motion envelope

Why did American eight-inch autoloaders suffer fewer jams than the six-inch system?

The eight-inch installation operated through a more restricted motion range, while the six-inch design attempted the full range and therefore faced greater complexity.

The heavier projectile did not automatically make the eight-inch mechanism less reliable. The distinction lies in what each installation was expected to do. The six-inch system attempted a wider range of movement, increasing the chances of trouble. The eight-inch autoloader accepted more restricted operation and therefore avoided some of that complexity.