If you accidentally place a 20 gauge shell in a 12 gauge shotgun it will most likely cram the barrel. This can very seriously injure the person using it and the gun immensely.
The main way in which the railroads contributed to the end of the large buffalo herds was that "The railroad tracks were obstacles that the buffalo would not cross". It sounds silly, but the buffalo actually refused to cross the tracks for reasons that are still misunderstood.<span />