In the Diana Patent the barrel tubes were inserted from the breech, with the step

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I don't know how Manufrance fabricated the barrels

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Modified Diana tubes inserted from the front

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With a somewhat scary looking seam over time

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Beretta and the other Italian makers (modern Perazzi, etc.), Browning Citori, and many U.S. makers adopted the from the front technique

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Which usually works OK, unless it doesn't wink

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