Hydraulic press is not a good idea. Secure the frame and drive against the breechface with a long drift to knock it open. This after ruling out a broken ejector tying up the gun. The breech should unlock & open with this tactic even with a slight barrel bulge although a bulged barrel may push the barrel bushing out the front. Messing with a 250 ton press will likely destroy the gun. I can't even think of a way to fixture a pistol vertically on a arbor press that wont result in wreckage. Perhaps you should consider seeking help from a local pistolsmith?

Cheers
Bill

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Because they don't make a .46