The shot was recovered and mounted on a gold seal and presented to Tsar Nicholas II as a gift. Photo Credit: Wartski 

It may look innocuous, but this tiny lead ball is thought to have triggered a rebellion that saw millions of Russians die and gave rise to the world's first communist state.

When the ball of shot narrowly missed hitting Tsar Nicholas II after it was fired from a cannon in 1905 in St Petersburg, it is believed to have set in motion a chain of events that culminated in the Russian Revolution.

Now its unique place in history is expected to see the grapeshot ball - which has been privately owned for almost a century - fetch up to half a million pounds at auction.

Although an investigation later found the shot had been fired by accident, Nicholas II is said to have been convinced he had been the target of an assassination attempt.

Three days later, the Russian Imperial Guard opened fire on a crowd of striking workers and their families during a peaceful demonstration, killing almost 100.

This incident earned the Tsar the title 'Nicholas the Bloody'* and led to a decade of civil unrest that culminated in the Russian Revolution of 1917.

*Bloody Sunday is the subject of a new article to appear in Royal Russia Annual No. 4, to be published August 2013. The author, Andrei Mantsov takes a new look at the facts of this historic event based on documents from the Russian archives, ones that are continually overlooked or ignored by Western historians - PG.

The rebellion dismantled the Tsarist autocracy in Russia and paved the way for the creation of the USSR, led by communist revolutionary Lenin.

Tsar Nicholas II and his family were executed in 1918.

The shot was recovered from scene of the 1905 'shooting' by a Russian duke who had been standing next to the Tsar at the time.

He took it to famed goldsmiths Faberge where the shot, which measures 1.5ins in diameter, was mounted on a gold seal that was later given to Nicholas II as a present.

A member of the royal court took it with him when he fled Russia at the outbreak of the revolution.

It has been in private ownership ever since but has now gone on general sale for the first time through London antiques dealer Wartski.

The item could sell for up to £500,000 given its 'exceptional' provenance and Faberge seal, experts said.

Wartski's managing director Geoffrey Munn, who has appeared on the BBC's Antiques Roadshow, said: 'This is a truly historic piece and an extraordinary treasure.

'The provenance is quite exceptional and from a time that now seems so remote yet was in an age of the motorcar and electricity.

'The will to revolution was born from this ball and the events that followed it being fired.'

Nicholas II's grandfather had been assassinated by revolutionary terrorists in 1881, and when he became Tsar in 1894, he used severe measures to subdue resistance movements.

But by 1905 he was seen as a weak leader, and on January 19 that year he concluded the grapeshot fired from a cannon was at attempt on his life.

This grapeshot ball is said to have missed him by three feet while another shattered a window, showering the Tsar's mother, the Dowager Empress, with splinters of glass.

© The Daily Mail. 27 February, 2013