This may be a result of several factors. First check to see how old the latex rings are. If they are older than one season, and haven’t been stored properly, this could be a cause.
Secondly, if they haven’t been stored properly, being left in the sun or outside with varying temperature, this will deteriorate the latex and result in breakage. Signs of age are discolorization of the band and signs of cracking. Better to be safe and use a newer band then risk possible problems with and old band.
Every batch of latex bands vary slightly in thickness. In most cases you shouldn’t have to worry about stretching the band back as far as it can. But occasionally, if you are Castrating a larger Bull, then one batch of bands may vary from the other.
Other causes maybe from Castrating in cold weather, and the rings are cold, this may cause them to break. Be sure they are kept warm somehow, such as a heating pad or some other way.
Check to see if the operator utilizing the Castrator isn’t mistakenly hitting the handle used to cut the band. It took me awhile to learn not to hit this when I first started Castrating.
Make sure, when installing the band, that it is stretched tightly between the two spreader bars.
Lastly, if you are Castrating a larger animal, the band may just be stretched as far as it will go and just break. Try not going back as far, maybe only 3/4 of the way back, crimp, then continue pulling the band as far back as possible, then cut. The band will continue to pull through the clip, even though it has been crimped. Then if the band breaks before it is cut, you’ve saved yourself the loss of a band and possibly a clip.