Jack, Remington regularly used the "decarbonized" designation on its early fluid steel sxs. I recall discussing it here before, but I don't remember whether we came up with a consensus recommendation on what one should shoot in those guns. That gun may well be old enough that standardization on shell length hadn't yet occurred, because the old "short tens" were 2 7/8", and the modern "long ten" is 3 1/2". If someone has service pressure data for the old 2 7/8" 10's, I think that would be your best answer.
