One from my collection.

Case is a fraction over 3", overal length is 3.84"
Comparison round is Elley 12gauge 2-3/4" roll crimp buckshot (2-15" closed)

Headstamp sugests Australian manufacture

Projectile is solid, blunt and made of hardish metal (not magnetic but certainly not lead - Possibly some type of zinc alloy?)

Note that the projectile is not centred, and is considerably undersized for an 8 gauge. Exposed section measures about .654" (8 bore lists at .835") All those I have are slightly loose and wobbly.

Looking down past the crimp it appears the projectile has a shoulder below the roll crimp that is closer to bore diameter.

These were used to break up slag or clinker inside opperating furnaces by firing through the inspection hatches or feed doors (EXCITING I would think)

Finally got pictures on as well. Now just need to get smilies right and I will be happy.