Howdy
Sorry I don't have a photo of a New Vaquero cylinder chambered for 45 Colt, but perhaps this photo will help.
Left to right in this photo the cylinders are from an Uberti Cattleman, Ruger (original model) Vaquero, and 2nd Generation Colt Single Action Army. All three cylinders are chambered for 45 Colt.
The revolver you looked at probably looked similar to the Colt or the Uberti. On the Colt cylinder, the metal at the thinnest portion between the chambers is about .040 thick. The metal on this Ruger cylinder is about .060 thick. Surprisingly enough, it is not how thin the metal is between chambers on the Colt that limits its strength, it is how thin the metal is between the cylinder locking notch and the underlying chamber. It is less than .040. I measured one the other day, but have now forgotten how thick the floor of the notch was. When one lets go, that is where it usually ruptures first.
No, neither the Colt nor the New Vaquero is meant to only shoot Cowboy loads. Current SAAMI spec for maximum pressure in the 45 Colt is 14,000 PSI, purposely kept low because of some of the old guns out there. There is no official SAAMI spec for cowboy loads, but they will most likely be less than Max SAAMI spec.
There are those on this board who will tell you the New Vaquero can take more, but Ruger is adamant about restricting the New Vaquero to SAAMI max spec loads. But it will digest any commercial loads made to SAAMI standards just fine.
A new Colt SAA, not an old one...
The Colt SAA has been factory warrantied for Smokeless powder since 1900. Any Colt in GOOD CONDITION that was made after 1899 will take Smokeless powder loads that stick to SAAMI specs just fine. From 1873 until 1900, it is recommended they only be fired with Black Powder.