Ron - you mention you will have to pull it apart to see what you have. If you have not pulled it apart yet, how do you know the bullet is longer? Are you going just by the Position of the case cannelure to the nose of the bullet? the bullet could possibly not be entirely seated. I have a U.S.C.Co. 17 dummy with GM bullet that does not appear to have been tinned. It has the same blind, empty primer pocket. However, the bullet jacket (coreless) is seated deeper than a normal ball round for a shorter overall length. I have a similar dummy with tinned bullet with core, same height cannelure, but a longer overall length, about the same as that of a loaded round.
I have never heard of or seen a dummy with miniature dice inside either, but I do have three different dummy rounds with U.S.C.Co. 17 and 18 headstamps and coreless bullets, with patriotic emblems attached to the case side, like souvenir dummies. One with a “17” date has a GM bullet and a copper primer cup (snapped). The other two are dated “18” and one has a GM bullet , and “18” date and a primer pocket with flash hole. The other also is dated “18” but has what appears to be a nickeled bullet jacket, not tinned, and a empty blind primer pocket.
The normal U.S.C.Co. military dummy is tinned all over, has an unsnapped inert primer cup (as originally manufactured - of course you see them snapped as well), three fairly large holes in the case sides about half way between the case cannelure and the top of the extractor-groove bevel, and three stab-type bullet crimps, like the WWI Revolver loads in this caliber had. The bullets have a lead core and are tinned as well. Variations are found in the height of the bullet crimps in relation to the case mouth.