Stu Miller's spine calculator

[toolmaker]

Just got my arrows properly spined.  Wow!  I didn't believe spine was the issue because my arrows were coming off the shelf dart straight, left to right, but I couldn't tune out the porpoising.  The best I could do was a 3/4- 1" tear. almost straight up and down.  Normal nock point adjustments just made it worse.  I softened up the spine with heavier heads after checking my setup against Stu Miller's spine calculator.  Problem solved.  

 

 

The scent of blood arouses the senses like the smell of ofal, musk and menses.

[Old York]

Now that is very interesting!

Solving a  porpoising  problem by changing dynamic spine. I take it you were shooting through paper?
If so, what distance? What kind of arrow shafts? Were they fletched? Bare? Split or 3-under? Off the shelf or elevated rest? More details please! Thanks

[House]

How much of a cant were you shooting with?

Travis

[toolmaker]

Yeah, I didn't believe it either.  After adding fifty grains to my arrow heads I am now getting about a half inch tear straight up and down, with almost nothing left to right.  My knocking point is about 5/8 above square.  I shoot three under with about a fifteen degree cant.  The arrows are 2216.  I was not bare shafting, and my paper screen was about 6 ft away.