Su­per­po­sed bol­ting com­plex­i­ties

SA Jagter Hunter - - NEWS - By JA­C­QUES P BO­THA

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.

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