Jack,
My father used to compete in target shooting with .303" and 7.62mm rifle. As children, my brother and I used to go along from early 1950's onward. We used to go to many army ranges around Sussex and Kent, also to Bisley Camp. A local one was Hythe Ranges, back in the 1900's it was the School of Musketry, the range was all shingle, being next to the sea and you would often spot a live cartridge in amongst the pebbles, so nothing unusual, they having been dropped. One day we found one, a .303" and it was pre-First World War, a bit dented but not corroded.
Richard