How can I ensure my meatballs or chilli con carne sauce stays moist?

I've tried both lean mince and the normal supermarket own brand mince. I normally fry the mince in sunflowere oil until brown then add the tomatoes, onion, etc and simmer for about 20 mins. The last time I tried to make the chilli it came out with a grainy texture (not sure if that makes sense).