NT. Regarding the H&H 12bore Rifle,I did re-check the "CerroSafe" casting you & "Dad" made,against my brass chamber gauge(made to Specs' From "1954 Rules of Proof')The Gun...Pardon Me! RIFLE does have 3" (Three Inch) Chambers....Hope You, or Dad' can find the 'Specs" for 3" Black Powder Loads!!! cc