hello all, i am back again with another question which you all probably feel is a stup0id but however the matter, here we go. I am on the market for building an ar-15. there are specific parts and features i want and i dont want to spend the extra money for all the stuff i dont care to have so i am building it. i am stuck on one thing, caliber. i know it is a big argument this caliber question, or more a personal opinion. my question is this, at what piont does an ar-15 become an ar-10? what calibers can i pursue with the ar-15? what the difference in ar style rifles like ar-15 and m denoted rifle m4 or m16? it seems there is no info on this question on the internet available. please help my no understanding self out. thanks alot.