Large frame Safety Automatic ( it ejects the shells automatically when you open it. ) The H prefix was used on the large frame automatic from 1918 unstill 1941, Serial numbers H11401 through H24700 was used in 1919. The serial number is in three places, on the frame ( have to remove cylinder to see ), bottom of the trigger guard and on the grip under the left grip plate. The history of Iver Johnson is long and involved, far longer than I care to type, if you use the search feature and read all the post about the Iver Johnson you will gain a wealth of knowledge on the subject. If the gun is tight and in good condition it would be safe to fire , using the 38 S&W cartridge, NOT the 38 Special, which is much higher pressure. If there are any doubts about the revolvers condition please take it to a gun smith and have it checked out. best I can do, hope that helps, shoot safe.