The number of frames that you can get in a cassette depends on the thickness of the film. For cine film like Eastman 5222 this is 30 exposures. Trying to get more can results in the film binding particularly when rewinding. Still films will vary a bit but 36 exposures is used for a reason.
BTW, loading film requires the upmost in cleanliness on the loaders part. In addition cassettes do not last forever and need to be keep scrupulously clean. You can buy little brushes intended to clean between the teeth. They are excellent for cleaning the felt light traps in cassettes. They are made by Butler.