Bare shaft tuning: Why are the arrows nosing down?

[WhistlingBadger]

Bare-shaft tuning some arrows for my new bow.  Spine/length tuning is going as usual, but my arrows keep turning nose-down, no matter where I put my nock point.  I've gone from extremely high to extremely low, and it gets better or worse (I actually went high to the breaking point of an arrow), but the arrows land nose down no matter what.  I don't remember ever having this happen before; usually I can pretty easily find a nock point where they hit straight and don't porpoise.  Weird.

Any ideas what's going on?

[Eric Krewson]

I have that happen a lot, at first I found it disturbing but since I was looking for right and left nock position to determine spine I ignored the tail high position.

[WhistlingBadger]

Hi, Eric.  Yeah, it doesn't keep me from getting the spine right, but it seems like it will affect arrow flight and penetration, and with this low draw weight, it needs all the help it can get.

[Pappy]

Mine always seem to tail high bare shafting, I just get the left /right good and set the knock as close as I can, then fletch and adjust the knock setting, works great, I figured it was the weight forward that causes that with no feathers on the shaft. 
 Pappy

[WhistlingBadger]

Yeah, that's kind of what I ended up doing, Pappy--Got it as close as I could, then got some feathers on and did the final adjustments.  Seems to be OK.  Never had that happen with my other bow, though.  Kind of weird.