Hi,
Fixing poorly installed set triggers is about the third most common task I am asked to do by clients coming into my shop. Most have double lever triggers that "theoretically" can fire the gun set and unset. The most common complaints are that the front trigger pull when unset is horrible, mushy, heavy, lots of creep etc. The second most common issue is they cannot cock the lock without first setting the triggers. There are other issues that concern the poor quality of many commercially-made set triggers but I'll ignore that for now. I will focus only on double lever double set triggers because they are the most common. The first step to inletting your set triggers to their best advantage is a good and precise drawing of your gun showing the layout. A good drawing will save many tears and kludge-like fixes later on. You need to take into account the position of the lock sear, the length of the levers, the final length of pull you require, and the height of the levers. That is much harder without a good drawing. The second step is to forget about the rear lever. Just make sure that lever will hit the sear but where on its top edge that happens matters not at all. Focus on the front trigger almost like you would a simple trigger. Try to position it so the sear hits the lever bar halfway or slightly forward of halfway. On some commercial triggers that can be hard to do and you have to move the contact point back. Just try and keep the contact as far forward as you can and still have the rear lever hit the sear when fired. Now one of the issues that pops up is when you set the rear trigger, the front trigger lever pops up a bit as the set trigger catches it. That "pop up" prevents you from positioning the front trigger lever directly against the sear like a simple trigger. It has to be a little below so the lock can cock. If it was a simple trigger, it would rattle. By positioning the contact point of the sear with the front trigger lever as far forward as possible while still allowing the rear lever to hit the sear, you can minimize that space below the sear required to allow for the for the pop up. The further back the sear hits on the front lever, the more pop up space is required giving the unset front trigger more creep. Finally, when builders can't cock their locks without setting the triggers it indicates the front or rear lever is too high and needs to be ground down. In most cases it is the rear lever that interferes when unset. That lever only has to be high enough to strike the sear so grind it down as far as needed to allow cocking the lock without setting the triggers. If you have to grind down the front lever, so be it but you will increase creep when the trigger is unset.
dave