When the british introduced the 1853 Lee Enfield, the cartridges were greased with animal fats so they could slide down the barrel easier. However in the Hindu belief system it is very very bad to eat or even touch beef products, like steak, ground beef, or beef fats. And since the cartridges were coated in beef or pork fats, if they touched it, it would restrict their access to the afterlife or something similar.
Some also say that the leaders of the