I'm tuning a setup and I'm getting strange reactions:

With a 125 grain point it's showing weak and slightly knock high. Impact is about 8" right and a couple inches low. Here's where it gets weird. If I increase point weight to 175 grains the impact is only about 2" right and it's no longer showing nock high. This is just the opposite of what I'd expect.

Does anyone have any idea what might be causing this?

We know increasing point weigh further weakens the shafts. If you make a change and don't see a change, that means you went the wrong way. Seeing an improvement by going up in point weight means they were over spined and hitting the riser to start with. You went up in weight and saw an improvement, keep going!   ....O.L.

OL,

Thanks for the suggestion and advice! I had the same thought about the arrow hitting the riser but I'd never heard of this or experienced it. I suppose this is similar to an extreme nock low setting that causes the arrow to hit the shelf and give the appearance of nock high.

I'll try going up to 200 grains, then 225 and see if that helps. The arrows I'm experimenting with are the Axis with the internal footing we discussed on the other post so I may have increased spine too much.

"I had the same thought about the arrow hitting the riser but I'd never heard of this or experienced it."

Scott, you never read my tuning page then!    Yep, it's exactly the same as nock point too low, it gives you the opposite indications. If that's what's happening and you go up in small point weight changes, at some point it'll jump from shooting right to left, further increases in point weight will move them back to center and further right if continued. Or you can jump way up in point weight and hope they are weak so you can work back down in point weight till they dial in. Just one step at a time....O.L.

Do you still have them full length or did you cut them the length you wanted to start????

I know w/carbons, you sometimes have to make a choice of long arrows or very heavy tips.   I like a better trajectory so shoot them about 3 inches long.

OL,

It's official, the shafts are a bit too stiff with the 3" parallel carbon tube IF and they're hitting the riser as you thought. I've got to make these work with 180 grain broadheads and a shaft with no IF is way underspined with that weight. I'm going to shorten up the IF to 2" on a couple of new ones I'll make up today and see if that gets me closer.


LKH,

My draw is so long the only option I have is a full length shaft so I don't have the option of cutting them shorter to tune. I'm shooting 300 spine carbons at 33" and they're underspined so I'm experimenting with gluing a short section of carbon into the front of the arrow to effectively shorten it up and make it act stiffer.

If they are a bit stiff, you can add weight at the nock.  

Not familiar with the IF???

QuoteOriginally posted by LKH:
If they are a bit stiff, you can add weight at the nock.  

Not familiar with the IF???

IF im not mistaken adding weight at the nock end will stiffen a shaft.

The "IF" is an internal footing. I'm using a short, 2" to 5", length of carbon tubing glued into the front of the arrow. The IF makes the front of the shaft extremely stiff and makes the arrow act stiffer, I shoot full length shafts so I'm effectively shortening the working spine of the shaft; the shorter the IF the closer the arrow spine is to what's marked, the longer the stiffer. I draw in the neighborhood of 32" so finding a shaft that's stiff enough to shoot heavy points is nearly impossible which is why I'm experimenting with the IF.

I could add weight to the nock end but I'm trying to get a somewhat high FOC so the weight on the back of the arrow would negate the heavy point.

With everyone's help I think I'm really close and I glued up four shafts today with 2" IF's and I'm hoping that does the trick. It appears for every 1" of IF added you can increase point weight by 40 to 50 grains.