I can't speak for other makes of guns, but the question was about LC Smith. My oldest 12 ga Smith, a 1901 hammer gun, has 2 3/4" chambers as do all of the 12 ga LC Smiths that I have ever checked. Parker supposedly made some guns with chambers that were 1/8" short, but those were for 2 3/4" shells also, with the thought that the shorter chamber sealed better. I don't have any early references that give the lengths of shells, so don't know all that were made.