What alternate/other caliber uppers

AR/M4 AR Technical Discussion
1

will work on a 5.56 lower? Any of the .50’s or the 5.7? Any others? What is worth the investment? Probably covered. Any links?

                                         dog
2

Start here: https://www.m4carbine.net/forumdisplay.php?f=10

Then…

http://www.68forums.com/

Buckaroo

3

Thanks, Buckaroo!
dog