Okay I'll try to explain a bit about the pretravel in buckmarks. First I'll explain what causes the pretravel.
Every possible gap that might be in between parts that affect the pull of sear cause pretravel.
Spot A has a little play. You can test this by holding the trigger in place and trying to move the disconnector back and forth. How much play is here is determined by the size of the hole and the pin. In my BM it's pretty tight and I could barely notice little play.
Spot B is has little more play in it. You can determine this by pressing the disconnector tightly against the frame and moving the hammer. This play is noticeable. But this also holds play from both the trigger and disconnector pin. But like tested earlier most of the play comes from the triggerpin moving back and forth.
Spot C/D aka the disconnectorgroove is the biggest cause of the pretravel. You can clearly see how much air there is in the picture below. It doesn't look like much but than again you have to think of leverage and the the movement of trigger is big. In my BM about 70% of pretravel is from the notch and 30% from the triggerpin. Now there has to be a bit of pretravel so that the notch in the sear can fit the groove in the disconnector.
Better picture of the gap
How to minimize pretravel?
That is a bit more trickier than overtravel. The disconnector spring is one of the weak link (in terms of adjusting) in BM since it has two jobs. It controls the upward motion for the disconnector as well as backward movement of the disconnector (forward movement of trigger). Now if we start tightening the triggerpin (spot B) more of the "work" goes to the upward movement of the disconnector and the trigger might not return forward fast enough. And if shooter tries to shoot fast it might be that disconnector didn't move far enough to catch the sear. So modifying the triggerpin is something tha could be done but changes have to be really small and are difficult to manage. Trying different pins might work.
Another solution is to add more material to spot D. Now how to add and how much is more of trial and error. Problem that arises is that fitting the searnotch to fit the gap is difficult. You can see that Spot C has a little roundness in it. filing that part is you could get the disconnector to catch a bit better. Here you just have to be careful not to file too much so when pulling the trigger you could "slide" the disconnector lower and not release the sear. Also you need to note that filing C increases pretravel. So filing incorporated with adding more material is a way. Just not something that I would suggest for the first try...
Now lets return to the trigger. This is where the movement is. If the pretravel is exessive you could try to put a small piece of tape in the frame over the front part of the trigger. This would prohibit the trigger from moving forwards. But be careful not to put too thick tape.
Adjustable pretravel? Create a new trigger that has a long "upperleg" and drill/tap a set screw there. There really aren't any easy ways to do it, unfortunately.
Hope this helped something and my mind didn't wonder too much from place to place. And sorry for spelling errors etc.
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