I was just looking around at the "photos of your AR's" thread and I saw one lower receiver that said it was multi-caliber. Is a rifle capable of firing different caliber rounds, from the same barrel? If you can, what is the range of rounds and how could you figure this out. Im used to shotgun shells where, you can't or really wouldn't even want to try to shoot any shell other than the appropriate size. Less experienced with rifles, and I guess this question could apply to pistols as well, just looking to beef up my fundamentals, thanks for the information.