Hello,

I know there are several claibers now in the AR15 style rifle including .308, 9mm, 10mm, 50, etc.?  I am in the planning phaseof building my first ARs and have been toying with the idea of owning  ARs with diffferent calibers.  I have already bought several stripped lower receivers in anticipation of my builds.   I plan on my first build to be 5.56mm.  Which  calibers can I build or buy as a completed upper that will fit on a standard lower receiver.  Are there any with minimal modifications involved to the lower receiver?  Is it just a matter of buying an upper receiver and barrel with a different caliber?  Or are there specific caliber lowers receiver that I would need to get? Thanks for your help.

www.ar15.com/forums/topic.html?b=1&f=5&t=338611

M4Madness......... Thanks for the link!