Question

Why did the sepoys refuse to use the new cartridges

Answer 1

They refused because :
It hurt their religious beliefs
The cartridges were made of pig fat and the soldiers had to bite it to use them.

Answer 2

muslim sepoys refused because the grease used to seal the cartridges contained pig fat. these cartridges had to be wrenched open by someones mouth. pig fat is unlawful is muslim: religion(islam)

hindus refused bcoz the grease also contained cow fat aswell and hindus refused to use them due to this