I have a Bostitch f21pl nailer that has served me well for at least ten years. However, it has always bothered me that it would not "contact trip" and I had to depress the trigger each time. Well, I found a part from Bostitch (CNTK5) to allow it to do just that. I installed it tonight and it works, but the problem I am having is that unless I am very cautious to only have a very brief depression of both the safety and the trigger it fires two nails, resulting in one not going in all the way or jamming the gun. I can't find anything in the manual that addresses this. I tried adjusting the depth and the air pressure and it did not make a difference. Thoughts?