Scooter, I shoot a .40 Kimber and a 9mm SA in ESP. Since all mags changes are done from cover,exception being the Classifier, I don't think it makes much difference. My Kimber holds 9, the SA 10. You have to load to the max on the first mag anyway. 9 +1 or 10 + 1. Not all stages are 18 rounds, some are as little as 6. Unlike IPSC one cannot leave partially loaded mags on the ground. Expending extra rounds down range just to get to slide lock can get you in trouble also.