An ancestor in The Royal Artillery you say?
Other abbreviations you might find in unit titles are:
HAA Heavy Anti Aircraft
LAA Light Anti Aircraft
SL Search Light
The RA museum is in South London at Woolwich. Firepower!. They have excellent archives, but you need to make an appointment to visit the reading rooms. The museum is well worth a visit if you have any interest in the military as it is full of big noisy stuff and rockets.
If you know which unit for ancestor served in (probably detailed as a Battery or Bty), you can find out where they were and which battles they fought in. Watch out though! A Battery usually has a number, but you can have the same number applied to different Btys with a suffix such as HAA or LAA.
An excellent set of books were (and are still being) published covering the history of the Gunners from WW1 through to the mid 50s. They also cover Indian, Australian, NZ and Canadian Army units along with some others. They are all published under the auspices of the Royal Artillery Institution in the History of the Royal Regiment of Artillery series.