Royal Horse Artillery. Date range - late 1800's. Maker / backmark - unmarked. Here is a very nice original uniform button. Listed in good faith and to the best of my knowledge and abilities.
Army Button Probyns Horse 5th King Edwards 19 mm Gaunt Early 1900's
Irish Army Button Royal Dublin Fusiliers Late 1800's QVC Firmin 19 mm
Irish Army Button Royal Dublin Fusiliers Late 1800's QVC Hobson 19 mm
Irish Army Button Royal Irish Rifles 1800's QVC Hobson 19 mm
Irish Army Button Royal Irish Regiment Late 1800's QVC Firmin
Victorian Royal Horse Artillery Officers Large 22mm Button by William Jones & Co