The number of times you can reload a case depends on many different things. If you shoot light loads, they can last nearly forever and you may not have to trim them more than once or twice. Hotter loads will cause them to stretch different amounts depending on the load, case life will shorten relative to that. The amount you have to resize them each time will be a big factor as well. If the chambers in your cylinder are a bit oversized and your dies have to rework the case walls much, it will shorten case life significantly and cause the need to trim more often. The amount of crimp or the amount of bell you apply to the case mouth will work-harden the brass and cause it to split after just a few loadings. Also the brass alloy used by a manufacturer will cause the case life to vary - even lot to lot.
