Because the Germans lost the First World War, they were required by the Treaty they signed not to make handguns with barrels over 3.9" long. Because of this the Mauser Broom Handle pistols they made during the 1920's had the short barrels your referring to. I don't believe either the Mauser factory or the people in Germany used the term "BOLO", for the post W W I Broom Handles. This is a American usage/convention thought up by probably the same enterprising dealers who foisted the name of "Black Widow Luger" on naive collectors.