I have an E grade Lefever from ca 1887 in 10ga whose chambers also measure 3". This is a 32" 10lb gun. I also have some old 10ga shells which I am most certain are original factory loads which are 2 5/8". I do not know for certain when the 2 7/8" shell was standardized, but believe in the early days 10ga guns & shells were available to order in lengths at least from 2 5/8" to 3¼" in 1/8" steps. I suspect these 3" chambers were original chamberings as would have been little call for a re-chambering to that length after standardizing.
