John,
Not sure what happened when you connected but I tried the links and they worked fine. Both links go to projectiles that have lead looking sabots and both have factory made lands on them. One is a bolt (1st link) and the other is a shell (2nd link) Both of them Jack calls an experimental Parrott. The bolt in the first link is exactly the shell I posted. Mine has in various places the numbers "9" and "92" stamped on it in addition to the "10".
My guess is that as Jack said it is experimental and he was testing the use of a soft metal to see the pro's and con's. Many other designs (Archer, Dyer, Hotchkiss, etc.) used lead or some soft metal successfully and you have to figure Parrott at least tested it.