What would be the most likely cause of this. I just had new strings and cables put onmy bow, tuned perfectly, (by a guy with the exact same setup). My field tips are flying great but when I put on bhs they start nose-diving out past 25-30yds. I am trying to shoot wac ems but also tried several other types and they all did the same thing. I have been consentrating so hard that I believe my form and shot sequence has never been better. At 20 yds they are pretty close to bullseye but they drop about 4-5 in at 30 yds and 7-8 in at 40 yds. The arrows also seem to move up and down when flying. I'm shooting around 260 fps with a 420 gr gold tip 7595. like I said I'm busting nocks with field tips. Also the wac-ems dove the least. thanks.

http://www.broadheadtests.com/TUNING.html

I assume you mean your broadheads are not shooting to the point of impact as field points. This is pretty common. As for tuning, you may think your bow is perfectly tuned, but it isn't. Porpoising is usually a sign of an improperly located nocking point or underspined arrows. In your case it sure isn't an underspined arrow.

I'm guessing that by tuned you mean shot through paper and getting bullet holes. OK, paper tuning is just a rough place to start the tuning process. It tells you how your bow is leaving the bow, but tells you nothing about what is going on down range. This is where broadhead tuning can help. And when paper tuning you need to check it at several distances. If you are tuning for a bullet hole at a particular distance it si tuned for THAT distance only. Move the paper a few more feet away and it may show a different result. And much over about 10 yards doesn't mean squat as the fletching is taking control by then anyway. That's just one reason I consider paper tuning a waste of time.

What do I do to move my nocking point down? There is some serving on the string that won't let me slide my loop down any more. Can I VERY CAREFULLY cut away some of the serving to slide it down and if so then what can I do to keep it in that position??? Thanks again.

You can try gripping the string tightly and turning the loop like a nut on a bolt. It may work. Depends on how tight the serving around it is. Failing this, yeh, you can be careful with a sharp knife or razor blade and cut the serving in order to move the loop.

I particularly like the idea of "screwing" it on the center serving as this allows for more precise and controled movement.