The gun is marked CAL. .223, which kinda indicates .223 REM.

However, so is my Ruger Mini-14, and talking directly with Ruger I got this answer:

"The unique Ruger receiver roll marking system of CAL. .223 for their Mini-14's should not be confused with norms associated with specifications for the .223 Remington and 5.56 NATO.  Every CAL. 223 Mini-14, with the exception of the Target model, is chambered for the 5.56 NATO, with all measurement, leade, and chamber pressure specifications certifiable thereto.

The roll stamping on the receiver is marked CAL. .223 to distinguish it at a glance from their .30 and 6.8 Mini's, but that is NOT a chamber specification. If you will note, the roll mark does NOT say .223 Remington, which is a chamber designation for the civilian variety with all its lesser pressures and shorter leade."

So, back to my Colt. What are the chamber specs? .223 Rem, or 5.56 NATO?

5.56.

Does the barrel have anything on it?

No, it won't.  Colt didn't the caliber on the barrels of SP1s.  That didn't start until the A2 l line started up.

All* Colt Ar15 rifles and carbines are chambered in 5.56mm NATO despite the .223 caliber stamp on the receiver.

* - Colt did make some rifles and carbines in .222 Remington for export to Congress that forbid private ownership of guns in "military" calibers.  Sometimes one can find any example in the US.

m-193 ball

Thanks all!

My 1983 SP1 says .223