Im guessing nothing. but is there a collect-ability one way or the other.

Rareness? Resale value? Collect-ability?

".223" marked were earlier Colt manufactured. There were both large and small stampings of the ".223", the rest of the stamp/rollmark being the same size. I believe the larger stamping was the earlier of the two, but could be wrong. I couldn't tell you what year the variations changed, however. But, more knowledgeable folks will be around shortly, I'm sure. You may also try browsing around the Retro section.