I'm about to build my first SBR - I just want to make sure I do everything properly the first go round. I'm planning on having both 9mm and 5.56/.223 uppers. I know putting "multi" on the form(s) is probably a big no-no.

By putting 9mm, 5.56 or 9mm & 5.56mm on the form... will I have to worry about it getting kicked back?

thanks,