Mid 19th C breechloading rifle

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I wonder if any members can help me with the identification of this unusual mid 19th C breechloader I have just acquired .
It seems to be 577 calibre , the rifling appears to be 3 groove , and oddly the bolt is on the left hand side . It has a bayonet lug which nearly accepts a P1856 yataghan bayonet but not quite , though the muzzle ring diameter is correct for the barrel . It has superficial similarities with the Carter Edwards rifle of the 1860s but the bolt handle is on the wrong side . I can find no markings other than 1234 on the steps of the ramp sight . Any help would be much appreciated