I have tried and tried and tried to keep a good count by tracking spent primers. It is, for some reason, impossible for me to keep track of which box of primer came from which rifle. A very poor inaccurate answer is less than 200 shots per vent. More than 100; less than 200 is the best answer i can come up with right now. Some seem to wear faster than others. It may have to do with the length of the flash hole. I am not done collecting data and formulating conclusions. Many have written that they notice accuracy suffering after the flash hole wear to 0.035", so i just set them vent aside, and replace after it erodes to 0.035". I believe i have replaced vents with less than 150 shots on them.