If you have a rimfire semiauto pistol handy practice with it first. Get the mechanics down and then move to something with more oomph.
If there are Ruger Rimfire Series matches in your area it's a great chance to practice your double taps. One stage you'll see at most matches is named the "Double Tap" stage.
It requires two hits to the left plate, two hits to the right plate (not necessarily in that order) and a single hit to the center plate. The outer plates are rectangular steel of approx 12x18" and the center is a round plate approx 12". It's shot from 7 yards.
The best shooters in the world that have tried it have broken 1 second (about 9 or 10 guys in the US I think). My personal best has been 1.1 seconds, but I hover typically in the 1.2-1.5 range on most of my strings, with the occasional goof that sends me into 2+ territory.
Of course that's all with a .22 and but it's good practice for the mechanics........