VM-68 Double Trouble Trigger
The Double Trouble Trigger is a rare VM upgrade. The DTT replaces the stock VM's entire trigger assembly and housing. With the new assembly the VM will fire once on the back stroke of the trigger pull and again on the forward stroke.
This action is accomplished through the use of two secondary sears. The main secondary sear, the one that engages first, is a normal stock sear. The other sear is custom and the primary sear is a modified stock sear. There are also about 2 other springs used in the mechanism. If you think the stock VM's trigger is complex, this one is even worse!
The one downside to this upgrade is the trigger pull. To activate two sears the trigger pull is very long; at least twice as long as the stock VM trigger pull. The pull can not be shortened either by using the normal simple techniques.
Although this is a fairly sought after upgrade by many VM fans, I personally don't think it's worth the money as a 'performance' upgrade. Even with some minor trigger work you can reach a rate of fire nearly equal to that of the DTT. The going rate for a DDT varies greatly, but you can expect to pay $75-$150 for one if not more. Instead of spending the money on one of these you could put the money towards lighter internals which would also help with the ROF. As a collectors item it's worth buying, but otherwise, I'd spend money on other things.