[Jim McDougall]

Fascinating topic, and Capn, I can see why you've had your sights trained on acquiring examples of these.
It seems these BAR SHOT have a number of variations, which have been in use for a VERY long time. While their purpose obviously was to destroy rigging and masts as these flailed through the air and tore through these on impact.
The drawback was they were horribly inaccurate unless at close range......clearly not very aerodynamic.

This type of shot was known as 'dismantling shot' (often loosely nicknamed 'angel shot' apparently in a bizarre sense).

The 1728 edition of Ephraim Chambers encyclopedia"
"...round shot with a long spike of iron cast in it as if it went through the middle of it"
The 1743 edition revised, " two bullets or half bullets joined together by an iron bar, serving to cut down masts".
* interesting to see cannon shot referred to as 'bullets'.

While obviously intended for this use at sea, these projectiles were horrifyingly used against personnel on land as well such as against Parliamentarians in English Civil War and against Cromwell in Ireland at Seige of Clonmel 1650.

On Blackbeards 'Queen Annes Revenge' there have been 35 examples of 'dismantling shot' found thus far, of 4 varying types. Naturally it seems likely pirate vessels acquired an assortment of such armament in their 'encounters'.

The QAR images are from Queen Annes Revenge 1718.
The third from the Swedish warship Vasa, 1628.

It seems to me that much as with most artillery, guns (and certainly the projectiles and ammunition) these would be held in use for long periods. Deck guns for example might be in use for a century. As these 'dismantling shot' were somewhat troublesome perhaps their use was often deferred, and the regular shot expended as required. Possibly a reason some survived for a long time, and in some cases were among artifacts of later shipwrecks.