Bifurcated Lumps & Trunnions
Bifurcated Lumps - A locking system for over & under guns whereby the barrels are fitted with semi-circular hooks that hinge around trunnions on either side of the lower barrel. A pair of bolts move forward into recesses on either side of the barrel-set when the gun is closed. This system makes it possible to build an over & under gun with a sleeker, lower profile than possible when mounting the lumps, hook, and locking bites to the underside of the bottom barrel. Boss, Woodward, Perazzi and most Beretta Over/Under guns are built with bifurcated lumps. (Bifurcated, means split in two.)
Inside the receiver of an A&S Over/Under. The bifurcated lumps engage trunnions on either side of the knuckle, just above the cocking rods.
Trunnions on a cannon barrel
Browning Superposed and Merkel Over/Under guns, on the other hand, are built with lumps under the barrels and with the hook revolving around a traditional hingepin. While strong, this design results in a gun with a taller profile than does the bifurcated lump design.
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