Well, the Germans and US had a 75mm cannister round too. But, these are far smaller than historical ones used in the 19th century that went in smoothbore as large as 11 or 13" in the case of naval guns of the period.
As for small arms, the largest manufactured shotguns were 6 gage or 1 bore (that is, 1" in bore). These were often used for big game hunting like the famous Holland Nitro Express guns.

__________________
Truth is stranger than bullshit!