The center lug regulates elevation. The lug on the rifle barrel slides and pushes up or pulls down, depending on its position. The shotgun barrel, being far more rigid, is affected little if at all.

The slide at the muzzle is for windage on the Valmets. They are a great and simple design.

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Hunt with Class and Classics

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Acquit v. t. To render a judgment in a murder case in San Francisco... EQUAL, adj. As bad as something else. Ambrose Bierce “The Devil's Dictionary”