That is (as he said up there^^^) not a S&W. It is an Enfield- sidearm of the British Army. Tons refers to the pressures in proof testing. It is on caliber .38 S&W, NOT .38 Special. Brits used a 200 grain .38 S&W. They called it .380 Revolver.
Well made guns, safe with the correct ammo IF it is original condition- which we cannot tell over the internet. Get a gunsmith to take a look at it.