The Battle of Gallipoli was made up of British, French, Australia and New Zealand against a fierce Turkish Army. In the end, the allied side lost 46,000 troops while the Turkish lost 65,000 with the Allies retreating from the battle. (These two bullets were found on the battle field. There's some discussion as to whether or not both bullets were fired and were in mid-air during the collision or one was fired and hit the other while stationary.)
The Turks still consider their victory at Gallipoli to be a great, defining moment in the nation’s modern history. Eight years later, the Turkish War of Independence broke out, led by Mustafa Kemal Ataturk. Ataturk was a commander at the battle of Gallipoli.
The battle was also Australia and New Zealand’s first military campaign as independent dominions in the British Empire. It was a formative moment in the national consciousness of both countries.
Its hard for us these days to imagine, but at the start of WW1 horse-mounted troops and stone cannon balls were still in use (although the stone cannon balls were only used by rear echelon troops in really old forts that weren't expected to see action). By the end of WW1 we had air forces that fought in dog-fights, tanks, and chemical weapons.
edit: But since then (and even predating the conventions iirc 1901-1903) there has been a lot of development, even in the early years, to 'unstable' rounds, aka 'tumbling' rounds, such as the british .303 I mention below. They're FMJ, but have an uneven weight distribution, which causes them to decelerate unevenly on impact, causing a larger wound, particularly on exit.
It's likely, as you say, that it hit a round in a clip, and I would presume that the casing, charge, and active primer would have been removed at a later time to render the round inert. But, who knows?.