There are many calibers that fit the ar-15 and there are many calibers that fit the ar-10. In those cases it's just a upper swap retaining the lower. But ar-10 calibers will not fit into an ar-15 and vise-versa.
Look I like glocks. I've owned Sig's, HK's, 1911's, S&W, and other fine pistols but Glocks have been a favorite for me. Handguns without safeties are not dangerous. Idiots are dangerous.