I know the Chinese make fake 90% silver 1916 D dimes and base-metal "silver" dollars, but find it hard to believe anyone would bother with base-metal common date dimes. Back in 1940-41, a Troy ounce of silver was only worth around 35-40 cents, so making one out of an alloy with similar density, appearance, and wear characteristics wouldn't be much more lucrative than making fakes out of standard 90% silver.
At 35 cents per troy ounce (31.1g), and with a silver content of 2.25g per dime, the silver value was only around 2.5 cents back then. And Antimony would have been a bit too soft for coins I believe, one might even be able to bend an antimony coin in their fingers without too much difficulty (not sure though). All that aside, it looks pretty legit to me.