I don't think there is any difference in function regarding the number of holes in the cylinder. There is some limit to the fewest number you could have and still have the hand move the cylinder to the next hole. 5 seems to be the most you can get into the smallest diameter without wasting space, so the smaller revolvers have 5 holes. I have a couple of old H&R's one in 22 rf and one in 32 S&W, they are the same revolver, but the 22 has 7 holes and the 32 has 5, they function the same. I don't think reliablity is an attribute you can associate with the number of rounds they hold. Larry