This has been done in the past as a battlefield expedient during emergencies. In what is now South Africa in the 1830s there was a deadly fight between Trekkers (white settlers) and the Zulu nation at what is called, The Battle of Blood River and is considered the spiritual beginning of the new nation of SA. The settlers literally chained their wagons into a small sheltered bastion. Using their flintlock smoothbores as their primary fighting arm along with a few small cannon, they used nearby water reeds as a field expedient buckshot mold similar to, what is used here in this thread.
Miraculously they did not suffer any deaths save for 4 wounded men. And pushed back the Zulu masses after 4 massive attacks.
a true story
Edit: I do believe Pretoria was the leader of this wagon train. Hence they named the nation's capital after him in his honor.