You may be interesting in this recent thread:

Why didn't gun technology develop in China as it did in Europe since gunpowder was invented there?.

You really need to make your question more specific - is there a particular time frame you are looking into (12th century, 13th century)? Gunpowder was invented in China during the ~9th century, so from the invention of gunpowder to World War 2, you are looking at almost one thousand years! You can write an entire book on the changes in Chinese firearm technology during this period alone (which Needham has already done), so answering this question is kind of difficult.