Don't know what you mean by the bubble, so a picture would help. In general, anything that isn't symmetrical will be unstable and print paper all over the map. That said, some very minor defects are ironed out by sizing or by traveling down the bore, so it depends how severe it is. Because some defects can be internal to a bullet (you usually find those by weighing—a bullet that's too light will often have some dross or other waste from the melt pot in it), the only really sure way to know is with a bullet spinner. This spins the bullet to detect vibration indicating it is out of balance. Harold Vaughn describes how to make one in his book, Rifle Accuracy Facts, but you need machine tools and and air compressor and some electronics know-how to do it.