I've used leeches since they hit the market and love'em. They do wear out, but Ive found that some last alot longer than others, maybe minute manufacturing defects . I've had some that lasted as little 100 shots and others that lasted at least 600. I do know from past experience that once they are in place they cannnot be moved without taking tension off of the string otherwise it will damage them, drastically reducing the # of shots you will get out of them. Hope this helps.