This is the best system I know of for the outdoors. I sure works well with a backpack... http://www.7xleather.com/chest_holster
I make holsters for a living and I spend a lot of time in the mountains of MT, So I have made and tried just about every design there is in an attempt to be comfortable carrying my pistol... this chest holster is what I carry my pistols in.
I have Bianchi X15 and can say that it just does not work very well with a backpack's shoulder straps and waist belt, and it is no where near as comfortable as my chest holster.
I carry a 4" N-frame 44mag in mine with a 6 round cartridge slide and forget I have it on... with the 19 K-frame it will be a real compact package. I am kind of biased here since I make it...But if you order one and love it, please write a review...if you hate it, you just send it back