Hi Sergio .
This picture is on page 126 of ' The Zulu War A Pictorial History ' by Michael Barthorp. Unfortunately the soldiers aren't identified.The same book page on page 158 has a photo of Maj J.F Owen with the Gatling gun which he fired at Ulundi according the caption . On page 51 of ' Uniforms & Weapons Of The Zulu War ' by Christopher Wilkinson - Latham there is a photo of a Gatling Gun with some members of HMS Boadicea . Also the photo from page 158 of Barthorp's book is also in Lathams on page 28 which says Major John Fletcher Owen ( Bt Lt - Col ) Cmdr of No 10 Batt , 7th Bgde states he used it at Ulundi .
' Brave Mens Blood ' by Ian Knight has a Photo of the Gatling Guns from HMS Active at the reading of the ultimatum on page 50. Also page 198 has another group Photo with a G.Gun . Page 50 of ' British Forces In Zululand 1879 ' by Ian Knight / Scollins has the HMS Tendos detachment with G.Guns at Ft. Pearson , page 49 also gives you a drawing with the scumatics of the G.Gun.