22lr is kinda dirty. If you're going to shoot 20 rounds, might as well shoot 200. I think most manufacturers fire two rounds in their pistols before they leave the factory and include the casings with the gun in box and sometimes the target. If they shot lead bullets, you should barely be able to tell use from looking into the barrel with the naked eye. You might be able to tell something with a bore light, or if copper jacket bullets were used. By the way you describe things--sounds possible that the range had let someone try the pistol before in which case it would be a used pistol and should be discounted as such. Maybe a better way to tell on a semi-auto is to look at the slide rails on the slide and on the frame to see if that's more telling. Thing is, you should have said something about this when you were there, before you purchased--(buyer beware). If you took it back now, they could say you shot 2000 rounds through it and just didn't like it. Sometimes the facts aren't what we want to hear. I hope you figure out what's going on, and I hope you like your new-to-you pistol.