Not sure exactly when the term came about but it related to small framed ("J" by S&W) revolvers that were carried on the trail, woods etc, by many outdoorsmen. Usually of small calibre. The various 22 RF revolvers by Smith, "J" frame or 32 frame were also refered to as "Kit Guns" as they were light, could go into a small pack or pocket. My Smith is a 31-2 w/4" bbl. I had the adjustable sights installed for obvious reasons. Small, light, accuirate, it makes a dandy trail piece. I had looked for several years before finding a 4" bbl model. Don't know when they were discontinued in 4" but I think it was around 1972.