First off, keep in mind that all of this is my opinion, and what works for me may not work for you. To get the most from a double trigger, I believe conventional style shooting has to be thrown out the window. If you want pinpoint accuracy I suggest you squeeze off your shots slowly in a traditional manner. This technique is about putting a short, rapid burst onto a player-size target.
There are two parts besides the double trigger itself that help achieve a higher rate of fire while maintaining fairly decent accuracy. One of those is a vertical foregrip. This can be an expansion chamber, vertical regulator, or purposely made vertical foregrip. The foregrip is held strongly by the non-trigger hand, which bears the weight of the gun, and serves to point the gun. The other important item is a stock of some kind, whether a tank, or a purpose built stock. As in most cases the stock is used to steady the gun.
trigger hand is then rested on the main grip frame, with the part
of your palm nearest your thumb against the back of the frame. Here is
where I see some people make a mistake that leads to an awkward feeling.
They try to wrap their fingers around the grip frame in a traditional manner.
WIth this technique, you bring your top two fingers around and place the
of those fingers on the trigger. Here is where another mistake is
often made, as shooters will wrap their fingers across the trigger. The
tips of your fingers are generally more sensitive and that means you will
be able to "feel" the trigger better as it moves. This also gives your
hand a slightly
different angle and allows you to in essence "push" back at the trigger
as opposed to "pulling" it. This motion can be both smoother and
faster. What you are doing is basically using your fingers to push the
trigger back, with your palm absorbing the impact. Lower fingers
should be allowed to hang free. This allows them to move with your hand
as you fire. It's much more difficult to move your top fingers rapidly
if the bottom two are trying to squeeze the grip. The same thing goes for
your thumb, it should be allowed to float free. Remember, you are
resting this hand against the gun and want to allow it as much freedom
The next thing to do is to practice and feel. On mechanical guns, use the tips of your fingers to feel the "breaking point" of the trigger - the point at which the trigger trips the sear. Get used to the length of the pull and learn where the breaking point is, and when to release the trigger. Start off slowly, pacing yourself. A good steady pace will allow you to develop a feel for the trigger. Once you get used to anticipating the breaking point, increase your speed. Like most people, you will probably find that your middle finger is doing most of the work. Getting faster takes practice. You may find that higher speed is easier if you use short burst as opposed to prolonged strings. Try starting off with three round burst, then work your way up to 4, 5, etc.
final note: Trigger jobs can both shorten and lighten the pull, but be
careful about taking them too far. Sometimes a trigger spring that's too
light will not snap back quick enough and actually slow the rate of fire.
Click on the picture for a video of the above gun being fired