What sniper rifle was used during the Irish Revolution?

Answer 1

There were few rifles that would be considered "sniper rifles" as the term is used today. Most were simply SMLE rifles that were well fitted and had barrels that passed quality tests. Frankly, the Irish used what they could get, including American Springfields, Thompsons, and the odd German Mauser here and there, . Taking the period of 1911 to 1927 as the revolution, that would have mainly been any of the SMLE type rifles up thru Mk III, or the P14 rifle,

Answer 2

There really weren't any dedicated sniper rifles. The IRA used a mixture of Short Magazine Lee Enfield rifles, Mauser G98 rifles, and whatever else they could get a hold of. The Mausers were provided while the First World War was ongoing by Germany, as the Kaiser intended to create as much trouble for the British as possible. They were supplied to both Republicans and Unionists. Lee Metfords were also used, and an ad hoc mixture of civilian hunting rifles.
When you say Irish 'Revolution", I assume you're talking about the War of Independence (1919 - 1921), although the Revolutionary Period is considered to have been from 1912 to 1923, and would include events such as the Easter Uprising (1916) and the Irish Civil War (1922 - 1923).