Over-Under Locking Mechanisms

Locking mechanisms of Over-Unders can be very complicated like the Browning Superposed or they can be a highly refined and simplistic design liked that employed by Beretta. The images below illustrate the ones accepted by the shooting industry as the best available. The first one, and most simple, is the Beretta system. The Beretta system used on the 686 is essentially the same system used on their guns that run into the 10's of thousands of dollars. In other words, spending more on a Beretta gets you better wood and better engraving. Instead of machined, integral side lugs such as the Boss bifurcated lug system, Beretta uses notches cut into the top of each side of the action wall that receive matching lugs forged into the shoulders of the barrels. This is a very secure system that allows for a very shallow and narrow action which greatly streamlines the gun and reduces weight. Additionally, dual conical locking lugs extend from the action face into matching recesses behind each barrel shoulder. The conical lugs are replaceable with larger sizes should the fit become loose through extended shooting.

The second example is of the famous Boss Bifurcated Lugs which are lugs machined on the inside of each wall of the action that fit into recesses machined into the sides of the barrel lump. This is also a very strong system that locks up like a bank vault. It provides for a very shallow receiver but because of the lugs, the receiver is wider than the Beretta. You can see how the Beretta and the Boss systems accomplish similar things with a slightly different twist in design. Holland & Holland, Perazzi, Woodward, Fabbri, Bosis, Abbiatico & Salivinelli, all use the Boss system. Additionally, a lug extends from the action face and slides into a notch on the botom portion of the barrel lump.

The third, and my favorite, is the good old over-engineered system utilized by Merkel in their famed 303. You remember the Greener Crossbolt I described in the section about side-by-sides, well, if you add a Greener Crossbolt to each side of an Over-Under and include two crossbolts instead of one, you now have a Kersten Double Crossbolt. All crossbolts MUST BE ROUND in order to effectively transmit the recoil force around the entire diameter of the bolt. The square ones that are out there do not accomplish the same thing. In addition to Double Kersten Crossbolts, the good old Merkel 303 utilizes a Purdey Double Undebite as well as a system where the lugs of the barrels extend into recesses on the bottom of the receiver. I can think of no action design stronger than this one and boy do you ever pay the price for it. A new 303 will set you back almost $20,000.00