I have measured a two pre-WW1 Elsie 10 ga guns that measure 3 1/4" Chambers. I believe they were chambered for 3 1/4" brass shells from the factory. 3 1/4" 10 ga shells were listed in all the ammo catalogs and sporting goods suppliers of the era. Waterfowl hunters of the era commonly reloaded there own shells. The factory letters from Smith are only shipping records so they say nothing about specs except barrel length and grade.