The artist, year, or battle that this painting takes place?

The Battle of Bannockburn took place on 24 June 1314, which was long before hand-held firearms were in common use.

The painting is called "The Thin Red Line" and is by Robert Gibb. It was painted in 1881 and shows the 93rd Highlanders at Balaclava during the Crimean war. The original painting is in the National War Museum in Edinburgh Castle.

http://en.wikipedia.org/wiki/The_Thin_Red_Line_(18...

http://www.militaryartcompany.com/robert_gibb.htm

Your picture is a reproduction print of this painting.

Look this is only a guess. But it may be the Battle of Bannockburn - definitely it is a battle in which the Scots (they are wearing kilts) defeated the English. I chose this battle, because in a poem on the topic, the defeated King Edward is described as riding a white horse. See http://www.taynet.co.uk/users/mcgon/bannock.htm

If this is correct, then read about the battle at http://en.wikipedia.org/wiki/Battle_of_Bannockburn

You could also get a valuation - and they may will probably know the artist - if you approach one of the big auction houses - Christies, Sothebys etc - they will ask you to send a photo in the first instance and other details. They usually don't charge as they hope you will sell with them.