Edited sentence: 5 inches (12.7mm) to be a "destructive device".Additionally, just as with "high" or "large" caliber, there is no defined threshold separating "heavy" caliber from light or medium caliber.Another misuse is "heavy caliber".Correctly used regarding firearms, "high caliber" would refer to the ratio of bore diameter to bore length, or in otherwords a "high caliber" firearm would be one with a very long barrel.For a big bore diameter, it is more correct to say "large caliber" (one would say "large diameter bore", not "high diameter bore").In this aspect it isn't really a misuse.Since most modern firearms are not designated by projectile weight, this is a misuse.The US military considers anything less than 20mm to be "small arms" and the US government considers anything over.The most common misuse of "caliber" is the term "high caliber".The other use of "high caliber" is to denote a large bore size.This is also a misue because there really is no threshold separating "high" (large) calibers from small or medium calibers.This might come from the idea that a high caliber ratio of bore length to bore diameter resulted in better accuracy and longer range guns.This probably traces back to when guns (cannon) were designated by the weight of the iron ball they shot.This term is often used to denote high quality or superior people, products, or services