What do you guys consider good 2 shot groups by shooting double taps at roughly 20 yards ???  Also, what's the maximum range for shooting double taps???

Thanks.

Anything in center mass. As for range, I would say that any distance that you can accurately place 2 rounds in a vital area is your maximum range. All of the tactical defensive shooting that i do is under 25 yards and i feel comfortable placing 2 rapidly fired shots on center mass at that range.

I try double taps at soda bottles at about 20-30 yards. My first shot hits but I usually see the dirt kick up about 10 feet or so away from the target from the second shot.

How exactly do you shoot your douple taps? Do you focus mainly on pulling the trigger as quickly as you can or do you fire the first shot and then fire again the instant the target is back in your sight picture?

EDIT: Would double taps be easier to do if you had a lighter barrel?

a double tap is two quick AIMED shots.  for the second shot you may not focus on the sight picture but if you are just spraying and praying you are just wasting ammo.   The more you practice the faster your double taps will become.  focus on hits.  Speed will come with practice.  After all what good is unloading a magazine in 3 seconds if you don't neutralize your target?

I think the term for two very rapid shots is "hammers" and/or "double taps."  "Sighted pairs" would be for two rapid AIMED shots.