I'm very sure firearms skill helps with how fast you reload. At the beginning of the game the Good Pistol (the one you get in the tutorial) I used reloaded fairly slowly, but once my skill in firearms increased I was able to reload it very quickly.
Also, from my experience, the double barreled firearms only take one reload cycle to reload both barrels. At least, that's the way it works for my Dutch Doubke-Barreled Pistol.