If a guy had too much money laying around, didn't ming the added frustration, and his wife wasn't looking..... And so he decided to tune both 400's and 340's to the same bow, the 3Rivers Dynamic Calculator would seem to indicate that is very possible. Just a matter of changing lenght, pile weight, etc. so that the arrow(s) dynamic spine matches the bow dynamic spine. At least so it seems to me.

Is that correct? If you can get the same dyamic spine on two different spined shafts that the arrows should shoot fine/great out of the same bow?

If The DW, DL, arrow length, Point weight match up, I could see three or more spines matching up for a given shooter & Bow. Total arrow weight may vary dramaticly.

I would not likely get any point weight work with my 30 " DL & a 70 lb DW compound bow. Same DL & a 20 lb recurve & the 400 spine may come into play depending on point weight.

That is correct. I don't have too much money laying around and don't seek added fustration, but I have tuned both 400 and 340 spine shafts to shoot good out of the same bow. The advantage of the 340's over 400's is more point weight and more forward of center balance on the shaft. It also gives you a heavier arrow...

I have always wondered how you can use the 3Rivers Dynamic Calculator for modern compound bows?

I doubt you can the way it is currently (or Stu Millers version for that matter). These calculators were developed with traditional bows in mind...

My 45# Samick Discovery shoots very well with 32"/340 spine/250gr point, or 32"/400 spine/175gr point.


I've crunched numbers through the 3Rivers calculator, but actually shooting them seemed to be required to try different point weights to get the arrows hitting centered. Our individual differences probably introduce variables the calculator cannot predict.

I was not clear. I do have a compound, but am working up arrows for a Bob Lee takedown recurve.

That's what I'm finding, and hoped to have others confirm it which I suppose you have! The calculator are snazzy bit of math work and give reasonable close results. But the're not perfect.

You were plenty clear on using it for your recurve. I was responding to nimrodtracy's inquiry on using it for compounds.

They use to make straw like plastic tubes to add weight to carbon arrows without changing their spine. I would go that route before any other. I'm not a big fan of a lot of FOC on my arrows. I tend to think massively front weighted arrows are more about getting a too heavy and too stiff arrow to fly than about any needed extra penetration. I might experiment with it if I was hunting dangerous game but I know that even a 42lb bow with 9 grain per pound arrow tuned properly will blow right through and Elk. I know a guy who has killed several.

I've seen those available at 3Rivers website.

https://www.3riversarchery.com/3rivers-archery-arrow-weight-tubes.html

Weed wacker string works too

This is some funny stuff! It will certainly kill an elk put in the right spot. But that isn't the same as blowing right through an Elk!

I've seen way too many elk hit with much heavier modern and traditional gear with half the arrow sticking out on broadside shots behind the shoulder with ribs being the only potential to hit bone.

Yes Sir!

The newer and expanded version is the best bet. Knowing what results I get from a proven combination of arrow, length, and tip, I can run different set-ups to match the same dynamic spine numbers. Center shot measurement is a big factor.
Currently running Easton Aftermath carbons in .400 and Easton XX75 2216 from the same bow.