No, it's not normal. Colt usually marked the EXACT caliber on their guns.
You gun has:
1. Been reworked to .45 ACP
2. Been rebarreled with a .45 Colt barrel.
The only way to find out for sure which, is to send Colt $100.00 for a historical letter, which will among other things tell you what caliber it left the factory in.
[This message has been edited by dfariswheel (edited 03-03-2003).]