Superposed bolting complexities
It has taken about 70 years for the over/under (O/U) shotgun design, otherwise referred to as the superposed, to evolve and rise to its current status and position of prominence. The rise was slow, but the current domination of the O/U shotgun design is now beyond dispute – it has been holding all the clay target shooting records, including Olympic shooting records, for the past four decades.
The dominance of the superposed design came about as a result of a combination of five factors, namely the rise in popularity of clay target shooting; the imminent suitability and durability of the superposed design insofar as competitive clay target shooting is concerned; the prominence of clay target shooting in America, where shooters, used to single-barreled guns, could more easily adapt to the single sighting plane of the superposed design; the advent of the famed Browning B25 Superposed, the first high-quality, but (relatively) affordable, mass-produced O/U design and lastly the “Italian Renaissance” – whereby the Italians have come to dominate shotgun design, manufacture and execution in every respect, especially so in respect of the superposed design.
It is no understatement to describe the Italian engineering genius and artistry in this regard as having triumphed over all nations, including the once mighty English.
It is by no means a simple task to build, on a viable commercial scale, a reliable, highlydurable and elegant well -balanced O/U shotgun. Whilst the English were the first to achieve success in this regard, this did not happen overnight. Furthermore, the English have never been able to mass-produce such guns. Reference to the work of the authority Gianberto Lupi (*1) reveals numerous rare examples of early English efforts at perfecting the O/U design, most of which are impractical, awkward and also outright ugly – not something one expects from an English gun.
DYNAMIC STRESS IN THE O/U
The superposed design, as in the case of any double, has to contend with a triad of dynamic forces which simultaneously come to bear on the gun upon firing. These forces must be understood in order to appreciate the bolting complexities of the superposed design and the bolting methods employed.
The first is axial force which operates along the axes of the bores, attempting to longitudinally part the receiver/breach from the barrels. Then we have bending forces which attempt to bend and break the gun at the angle of the receiver, often leading to receiver cracking. Finally we have radial forces which attempt to open the gun against the bolting device employed, stressing same.
In addition thereto, and largely as a result of the substantial radial forces acting on the gun, the breach of some double guns has been demonstrated, through the application of sealing wax at the point of the upper breach/ barrel junction, to microscopically gape for a millisecond on firing – evidenced by the fracturing of the sealing wax. Gaping is undesirable as it dramatically
A Blaser F3 – one of the shotguns employing an underbolt with a single bearing surface. Prospective competition shooters should look for a gun with a well-engineered and robust locking system.