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 and Woodward guns are built with bifurcated lumps.
Browning and Merkel guns are built with lumps under the barrels and with the hook revolving around a traditional hingepin, as on the Merkel above with double Purdey underbites. While strong, this design results in a gun with a taller profile than does the bifurcated lump design.