What weapon wounded Dr. Watson during his military service in Afghanistan? and here is the account written?

In the first chapter of A Study in Scarlet, Watson mentions the injury in his brief account of his service during the Afghan war:

"I was struck on the shoulder by a link bullet, which shattered the bone and grazed the subclavian artery. I should have fallen into the hands of the murderous Ghazis had it not been for the devotion and courage shown by Murray, my orderly, who threw me across a pack-horse and succeeded in bringing me safely to the British lines."

Wikipedia describes a Jezail as "an Afghan matchlock or flintlock musket fired from a forked rest."

You're in luck because A Study in Scarlet can be read link on google books. The above excerpt is from the very first page of Chapter 1. :)

It was a rifle bullet named jizail