I was with 3RTR from 1972, in Fallingbostel and three tours in Ireland, until 1977 when we all moved to Tidworth.
This was about the same time as your grandad but as he was in a different sqn I didn't know him well.
Think this his him standing at the back.
The above picture would have been taken late 1974 during our tour in Armagh city and surrounding area.
We did our Northern Ireland training in a tented camp in Sennelager and had our own evening entertainment.
I was in 3RTR 1973-1979 and was in the same troop as Terry for a couple of those years. He was my troop corporal in 11 troop and I think I may even have been his loader/operator for some time. He was a gunnery instructor and from memory a general good all round Tankie! There are lots of photos of C Squadron on the Green Flash 3RTR site. He is in a good few of them.