Raimey,
Rim thickness & base taper will tell the tale. Measure the depth of the rim recess in the extractor & several measurement of base dia. starting in front of rim then in .25" increments. The D case will have most of its taper in the 1st 3/4" in front of the rim then taper becomes more gradual over the remaining length. These were thin rim cases (Note EXP39 pic provided above)


m-4