I can't seem to find much on these . The trusty Google search only provided a single hit here . Only vague sketch without a description seems to be available for any of the 3 . The 266s seem to be the same but with and without gas checks maybe 1 is an FP ?
257312 4 cav
90 gr RN
266469 1 cav
266324 1cav (IDEAL)
Being an Ideal mould it must have for 6.5 x 55 but somebody might know of another.