What does it mean if a guy shoots blanks?

Hi my name is Paula and I'm sixteen (turning 17 in three days) Me and my boyfriend have been together for two months and I'm pregnant. I thought because he was 20 he would be more mature and take responsibility instead he freaked out and started calling me names. He said the baby could be any ones and he shoots blanks. I'm positive its his baby because I have not been with anyone else. So what does shooting blanks mean?