I've found it to be very accurate as long as the info you're inputting is accurate.

 

I added 1gn per inch for the arrow wraps I use to the nock weight. Do you think that is an accurate way to portray that info?

 

Agree with bucco921, you put accurate numbers in, you'll get helpful/accurate information out. Also agree on weighing components individually if at all possible.

I've found the 3Rivers calculator pretty much dead on with the half dozen bow/arrow combinations I'm currently shooting. In fact, if anything the recommendation that the bow spine and arrow dynamic spine be within 2-3 points is very conservative IMO. In experimenting I've often been able to get good tune/flight with a difference as much as 5-6. More than that all bets are off.

 

Right now I'm 0.7 on the 1716 & 0.1 on the 1816 So, I need to decide on light (377gn 9.8FOC ) vs heavy (410gn 11FOC) arrow. Since ASA 3D is likely, light and faster seems better.

 

You should be golden either way as long as the guy behind the string is doing his part, lol. If this were me, I'd definitely lean toward the heavier arrow, especially if you have a notion to hunt with this setup (you mentioned BHs in your OP).

 

BH was referring to Brace Height. I have a compound bow for hunting.

 

3 rivers is accurate. Easton chart is good if you are using a plunger, but it will be about 1 Size too stiff if you shoot off the shelf. 1816 sounds right....

 

I agree. Easton has historically shown about one size too stiff for recurves and longbows.

 

It's pretty right on for me.

I'm using accmos shafts which are 20g lighter than these but the arrow that tunes and the chart is only 1/2 a pound off.

 

Honestly I've been pretty amazed at just how accurate it has been for me. Like NxNW said, I'm usually good within 5 either way.

 

The problem with the 3 Rivers Spine Calculator is matching a bow with what you have. If you don't have one of the bows in their list, you have to guesstimate what one of their bows would be as close to yours.

For Example: I have an ILF Hoyt Satori 19" riser with Uukha Gobi short limbs at 45#. There's nothing in their bow list that would come close....except maybe the Morrison, but that's just a guess to get me in the ball park.

I'm shooting Gold Tip Traditional 500 spine and cut them and changed field tip weights until I got good flight.
I have a 27.5" DL and ended up with a 29" arrow and a 250 gr. tip weight. Sometimes you have to make a few changes to get your setup to fit you. 💯

 

I find it surprisingly accurate even with my longish draw, but you need to take care of 'hidden details' like long brass insert length (which stiffen a bit even as they soften), and be very sure of your draw length (before release), and the center cut distance.

For long inserts, just define a Footer, set the length to that of the non-standard insert, and then set it to 0gn. Then be sure to just set the actual weight of the insert in the Insert section.

Even so you should allow for variables like string silencers and bow quivers, even stabilisers, to deviate 25-50gn of dynamic spine.

Best is to use the calculator to get a rough arrow build, and bareshaft tune with end/point weight to get it shooting sweet.

 

The problem with the 3 Rivers Spine Calculator is matching a bow with what you have. If you don't have one of the bows in their list, you have to guesstimate what one of their bows would be as close to yours.

For Example: I have an ILF Hoyt Satori 19" riser with Uukha Gobi short limbs at 45#. There's nothing in their bow list that would come close....except maybe the Morrison, but that's just a guess to get me in the ball park.

I'm shooting Gold Tip Traditional 500 spine and cut them and changed field tip weights until I got good flight.
I have a 27.5" DL and ended up with a 29" arrow and a 250 gr. tip weight. Sometimes you have to make a few changes to get your setup to fit you. 💯

There is always one guy who says the calculator is flawed because it doesn't account for his super whatever limbs and way past center riser. I would say the calculator isn't meant for that. I have always used generic longbow or generic recurve.

If you have one of the super bows, I would go to your bucket of spare tuning arrows and find something that flies straight. Then plug its specs into the calculator to get a dynamic spine that you know the bow likes. Now play with other arrows, lengths and point weights in the calculator to come up with a combination in a weight range you like that has the correct dynamic spine. Used like this it usually predicts withing 25 grains or so of point weight.

 

The key is ACCURATE information.

For example many archers think they know their draw length but have you ever really had someone watch you SHOOT an arrow to determine the draw length? That is the only way to actually know. Mark an arrow with a marker at 27, 28 etc. Then shoot your NORMAL way just relaxed and shooting arrows. Have someone watch to get a reference mark and weigh the bow at YOUR draw length. Some archers are very surprised thinking they draw 28 when is reality draw is 26. Big difference in poundage...

The key is to put in exact information on each variable and avoiding "guesstimating".

GREAT Tool that was developed.

The older version of the calculator had horsebow recurve that would probably work for a supercurve.

download is here for the older calculator.

Stu Miller's Dynamic Spine Calculator download page

This calculator was developed to aid the traditional archer in defining the appropriate arrow setup to match a given bow design. That formulas are derived primarily from modern deflex/reflex longbow and recurve designs based on actual shooting experience coupled with basic engineering principles.

heilakka.com

 

The key is ACCURATE information.

For example many archers think they know their draw length but have you ever really had someone watch you SHOOT an arrow to determine the draw length? That is the only way to actually know. Mark an arrow with a marker at 27, 28 etc. Then shoot your NORMAL way just relaxed and shooting arrows. Have someone watch to get a reference mark and weigh the bow at YOUR draw length. Some archers are very surprised thinking they draw 28 when is reality draw is 26. Big difference in poundage...

The key is to put in exact information on each variable and avoiding "guesstimating".

GREAT Tool that was developed.

The older version of the calculator had horsebow recurve that would probably work for a supercurve.

download is here for the older calculator.

Stu Miller's Dynamic Spine Calculator download page

This calculator was developed to aid the traditional archer in defining the appropriate arrow setup to match a given bow design. That formulas are derived primarily from modern deflex/reflex longbow and recurve designs based on actual shooting experience coupled with basic engineering principles.

heilakka.com

I feel my info is pretty accurate. I have taken measurements of DW @28"&27.5" and DL several times with a couple methods to make sure it's right. Even took measurements of my shelf/center cut with digital calipers along with calf hair plate. I also sit down and weigh out components or verify weights on manufacture sites. The only thing I had to guess at was to factor in arrow wraps since it's not an option on the 3rivers. I plugged in a known stiff arrow and my results were what I expected.

Yes, I have used the Stu Miller calc.

 

I'm looking at two arrows.
1. Jazz 1716, 29" with 85gn point
381Gn
10.3 GPP
9.6FOC
177FPS

2. Jazz 1816, 30" with 100gn point
413gn
11.2GPP
10.9FOC
170FPS

For indoor target and ASA3D, which one?

 

The heavier one. I would go to a 1916 with 175 or 200. Close range gaps are unmanageable for me with a fast arrow.

 

I have been looking at Eastons legacy shafts. Does anyone know what would be equivalent on three rivers spine selector. Have run the numbers with generic carbon, but am worried about messing it up. Shafts are pricy these day. Haven't made arrows in a while. Am thinking about their spine test kit, but havn't made up my mind yet.

 

Black Eagle Vintage are basically interchangeable with them.

 

Thanks. I have been looking at those as well. They are my second choice. Glad to know that they are pretty much the same shafts.