Hi All,  I was reading some posts on the AR15's and ran across a fellow referring to a 22 conversion for his AR that he carries with him when he goes to the range.   Maybe I'm dumb, but how do you convert a center fire rifle to a rimfire?  The idea interested me because I really have a lot of fun firing those little inexpensive shells. ha!  If any of you guy's could shed some light on this subject for me I would appreciate it.
Thanks,
Jim

Here is one link of many out there, Should answer your question.

.22 LR Conversion Kit

DPMS makes em, they sell for about $175 or so...  I have one.

It is a bolt replacement.  You remove the AR15 bolt carrier group and put in the .22LR bolt group.  Then you use a different mag that hold .22LR rounds but fits in the AR-15 magwell.

Conversion take me about 8 seconds.  :)