found a bit more info in a Ruger Forum:
The new Speer #14 reloading manual has a big bold caution in the 45 Colt Ruger & T/C only section. It says:
"Important Safety Note. Since we published the last manual, Ruger has replaced the origional Vaquero revolver with a smaller version called the New Vaquero. Ruger has advised the industry that the New Vaquero must not be fired with loads exceeding industry pressure standards (14,000 psi). If loading for a New Vaquero, use the standard pressure data in the previous data section."
