Great thread! Beretta 1938, MP28, and MP34 submachineguns[SMG]look steam punk but they are from the diesel punk era. Some firearms transcend both eras for example, the original M1911 .45 pistol is Steam Punk because originated before 1920. But the 1911A1, is a diesel punk weapon because it originated about 1925-ish[?].
Incidentally, the MP34 SMG is the Austrian one that is mentioned in 'The Great War: 1861'.