I remember many years ago, a thief in Birmingham, Al was stealing silver and making silver dollars himself in order to pass them.
Interestingly, his sliver dollars had more silver than the U.S. Mint ones did.
Their solution was to counterfeit U. S. silver dollars and run them across the border. The government looked the other way because the fakes were good quality and the Mexicans were careful to keep the silver content higher than the real thing. The little scam kept businesses on both sides of the border going.
No one knows how many were made this way but it was probably millions. The only problem was that the higher silver content caused the coins to wear faster. If you have a silver dollar that looks unusually worn, it was probably hecho en Mexico.