Hello! Unfortunately, the calibre is unknown to me. Yes 800 yards is along way for such a small creature but I can definitely imagine such shots being taken back then. The reason shorter shots are taken today is because the Gazelle is often chased with a vehicle until it is less likely to run....and then shot at a shorter distance. I actually have a pair of RW quality Eritrean Gazelle pick up skulls that I found in the southeastern desert near the Sudan border. So wish I were allowed to hunt them.