If your gun dates to 1872 I'd say your chambers are not original length. The British standard stayed 2.5" but a gun built for export to the USA after USA standard became 2 3/4" would have been built to that chamber length if specified by the dealer. In that time period I would think a hand built gun could be ordered with any chamber length a buyer wanted, but 2 3/4" just was not standardized even in America or Canada in 1872...Geo