Tuning question

[McDave]

I have been setting up a new Hoyt Satori bow for 3D, and was initially going to use GT Ultralight 600's.  I bare shaft tuned, and was getting perfect bare shaft flight.  However, in shooting fletched arrows, I noticed a kick up.  The arrows I was shooting were from a new batch of shafts, but the bare shaft was from an older batch.  I made a new bare shaft out of the new batch, and shot them side by side.  The old bare shaft shot perfectly, but the new bare shaft shot about 10-15 degrees nock high.

These are the things I have eliminated as causes:

1.  I usually shoot bare shafts with the quills attached.  I shot bare shafts with and without quills, and got the same result.

2.  I swapped nocks on the two bare shafts and the difference was less, probably because the nock on the new bare shaft was new and a little tighter, but there was still at least a 5-10 degree nock high on the new shaft with the old nock.

3.  I tried to shoot them blind, as far as possible, by having my wife hand one to me and not looking which one it was before I shot it.

The new batch weighs about 10 grains per shaft more than the old batch.  This is not inconsistent with weight differences I have noticed in the past between batches of GT arrows, and I don't like it, but they are still pretty good arrows so I continue to use them.

I would just shoot the old batch, but I'm about out of them.  I tried Victory VAP 600's, which tune well, so I switched over to them.

I didn't try lowering the nock point to see if that would correct the nock high in the new batch.  It is already tied and glued in, and works fine with the VAP's.  It is set at 1/2", and even if it gave me level flight at a lower setting, I really don't want to go below 1/2" because that increases my gap.

Any ideas why two shafts of the same designation would bare shaft differently?

[texbow2]

My guess would have been nock tightness. Same inserts? Same nocks?

Put both of them on a spine tester and see what that tells you?

Bisch

[Orion]

Yeo.  Those are the only two things I can come up with. Nock tightness or perhaps a difference in spine, all else being equal. Might you have slightly changed the fletching size/orientation? Fletching may be hitting the shelf more than it should, which could also be a spine problem as noted.

[McDave]

There is somewhat of a difference in spine.  The old batch measures .525 on my spine tester, while the new batch measures .500.  These are supposed to be .600 spine arrows, but my old spine tester was intended for wood arrows and may be calibrated differently than they measure spine on modern carbon arrows.  In any event, the comparison should still be valid.

To eliminate effects of nocks, I put identical new nocks on each bare shaft, and to eliminate effects of fletching, I shot totally bare shafts with no quills attached, although I normally like to use bare shafts with quills as I think that results in more accurate tuning.  About a 5-10 degree difference in nock high still exists.

I guess the spine difference must be the reason.  I always think of spine difference as causing a sideways deflection and not a vertical deflection, but maybe a change in spine effects both, and we just adjust for vertical and horizontal deflections differently.

[Orion]

McDave.  The reason I asked about fletch size/orientation was because you noted the kick on the fletched arrows.  Should have read more carefully.  The feathers helped you notice it, but likely didn't cause it.

Yes, carbon spines are measured differently.  A. 600 deflection weighed the way Easton does it, i.e., a 1.94# weight on the center of the shaft balanced on posts 28 inches apart, yields a spine of 52-53#.  

According to a conversion chart I picked up off the internet, your measurement of .500 using a 2# weight on an arrow suspended between posts 26 inches apart, yields a spine of 52#, virtually identical. A .525 deflection using the same scale comes out to about 49-50#.

So, first, you did get an accurate reading off your spine tester and the comparison between old and new is also valid.  Your new shafts are spined 2-3# heavier.  That really shouldn't make much of a difference, IMO, unless you're right at the edge.

I'm thinking as little as 10-20 grains more point weight would straighten them out, but this is mighty fine tuning. Seems quite sensitive.  Let us know what you find out.

[kenneth butler]

McDave if there is a spine difference in the shaft in the rotation of the arrow,weak or stiff spot, Wouldn't rotating the nock show it up?>>-->Ken