As the editor that removed the tag the first time I can give my reasons. 
 *It happened 165 years ago. Any documentation from day to day activities at that time are scarce and the information is very unlikely to exist. Even Gage's exact accident location is unknown. 
 *A few of the editors here are very knowledgeable of any known sources and would most likely have added this material before now. 
 *After working on construction sites where blasting took place in modern times, I know there is an art to it and there is no standard charge. It depends on many things, see Rock blasting. 
 *Even if you knew the exact amount of powder and composition you couldn't calculate the velocity accurately because you wouldn't know how much energy escaped between the iron and bore hole or even into the rock strata. 
 *I am not a fan of tags being in articles forever waiting for information that is almost certainly never to appear.