Quote Originally Posted by RCCrawler View Post
Now my question, if I register it with a .223 caliber, will I be able to switch it out at will to anything else? 9mm, 300 BLK, ect.
Yes as long as you keep a .223 upper around so it can be made readily available into the original configuration.

That said; I have an approved Form 1 with about 20 calibers listed on it - everything from .22LR to .338.