Calculating spine vs actual

[brucelanthier]

As I am still learning about this stuff I have a question about the calculated spine from Archer's Adv and the results I am seeing from the actual shooting.

I am shooting a CX terminator xp select cut to 28.75' (shaft only). It has a tcx nock, a cx insert and a 125g field point with 3 blazer vanes. With this setup I can shoot good groups (arrows touching)at 20-30-40 yards (haven't gone further).

When I shoot this arrow bare shaft at 20 yds it hits about 4+ inches left of the group. It is my understanding that this is a stiff spine.

Archer's adv tells me that I am underspined. I have entered my bow data and left it at the default.

Is there something I am missing here?

ORIGINAL: brucelanthier

As I am still learning about this stuff I have a question about the calculated spine from Archer's Adv and the results I am seeing from the actual shooting.

I am shooting a CX terminator xp select cut to 28.75' (shaft only). It has a tcx nock, a cx insert and a 125g field point with 3 blazer vanes. With this setup I can shoot good groups (arrows touching)at 20-30-40 yards (haven't gone further).

When I shoot this arrow bare shaft at 20 yds it hits about 4+ inches left of the group. It is my understanding that this is a stiff spine.

Archer's adv tells me that I am underspined. I have entered my bow data and left it at the default.

Is there something I am missing here?

One you shouldn't be shooting blazers unless you are on elevated rest.

You will have interference on the shelf. and propably get false indicating results.

Second, hitting to the left means stiff. But be careful here. This could be from your release. For me, a good crisp release, my arrows group great bareshaft or paper tuning. A bad release, you get results showing stiff.

Oops nevermind, thought this was traditional forum.

[Paul L Mohr]

When shooting a compound and a release there is no set standard. I use the bare shaft method to tune as well, but you have to keep in mind it is really intended for finger shooters, and more so for traditional equipment. If the program says you are underspined and your arrows don't group together chances are you are indeed under spined, regardless of what the standard is.

The only way to know if it is spine related is to change the dynamic spine of your arrow and see if it gets better. Turn your poundage up to make the arrow weaker and turn it down to make the arrow stiffer. Or you could add tip weight to make it weaker.

Another thing to keep in mind is removing weight from the back of the arrow also makes the dynamic spine weaker, so removing the vanes would make your arrow weaker as well. When I bare shaft tune I trim the vanes off but leave the base of the fletching and the glue. This keeps the weight and FOC very close to the fletched arrows you are comparing it with.

Have you tried any rest adjustments yet? It may be something as simple as moving your centershot slightly to fix the problem.

When I bareshaft tune I set everything so I am a hair nock high and my centershot is straight. Then I start shooting arrows. If they are off I make rest adjustments to try and bring them together. If you can't get them to come together or it takes a large amount of adjustment chances are your spine is off.

Keep in mind these programs are not perfect, and they are only as good as the information you put into them. And the more you tell them the more accurate they can be. If you were a bit off on the info you put in it then things may not be quite right. They are much more accurate than the charts and online calculators though.

Most have a way to synch the program to your bow. Like if you use the program to choose an arrow and discover it wasn't quite right and you needed to change tip weight or poundage to get it right you can let the program know that and "synch" it to your bow. I have OnTarget2 and it wasn't dead on with my Mighty Might, I had to up my poundage by 5 lbs to get it perfect. Now I have corrected the program to my set up and next time I decide to change arrows it should be much closer.

Also shooting 4 inches off could be bow torque, especially at 20 yards.

Paul