Note how the barrel assembly looks like an over/under shotgun? The recoil spring is in the top tube and the barrel is in the bottom one. When you tip the barrels up, that hook on the rear of the recoil spring assembly goes with them and so the breechblock is free to cycle without being under spring tension. A variant of this setup appeared on the Belgian Clement pistols that Smith & Wesson licensed for their original .35 Self Loader.
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