Arrow spine.

TheBigRedArcher · February 03, 2010, 01:08:00 PM

Ok, here's something to chew on guys.

I currently shoot a Robertson Falcon 4 recurve 53#@28" 62" bow. My arrows are as follows (please hold to remarks) Carbon express 250 cut to 29.75" with 12" of vinyl sticker wrap and four shield feathers on the back, aluminum nock adaptor and bohning t-nocks, fort he points I use 125 brass adaptor 145 steel glue-on point and 2 inches of a 2117 arrow for extra durability for a total point weight of approx. 290ish grains.

I have great foc weight and the arrows fly excellent. What bothers me is according to online calculations, my bow shoots these arrows at 155 fps (consistent) and total arrow weight being 681 grains, I get 36.34 KE foot pound of energy at impact.

I am thinking of going to the heritage 150's to see about a speed increase and thus a increase in KE if the combo works out. Is there a calculation to figure point weight or is it back to the drawing board testing different point weights until one works?

TBRA

Orion · February 03, 2010, 01:20:00 PM

Read the Ashby research on this site. Kinetic Energy is a poor predictor of penetration. One might say it's a worthless predictor of penetration. Momentum, of which you will have a high degree with your set up, is a much better predictor of penetration.

Bjorn · February 03, 2010, 02:48:00 PM

Even if there were it would screw up the allowance for spine. Like Orion said, KE if for the speed and knock 'em down crowd. Momentum is for penetration folks.

davesonic444 · February 03, 2010, 04:40:00 PM

I'm going to suggest less head weight.The setup you describe is underspined for your bow.You can drop 100grains and increase speed and have a better tuned arrow.According to Stu's calculator you would have 9.5grn per pound of draw wieght and arround 180 in speed.40.7 # KE

TheBigRedArcher · February 06, 2010, 12:10:00 PM

Dave,

Thats the plan as it stands right now. I am going to try a lower head weight (by approx 100gr) but I at this time have great arrow flihgt with the CX heritage 250 so I am goit to also try the CX heritage 150. The local archery shot owner and I are going to play with it and see what we come up with

Bjorn, Yes, I agree with you. Momentum is penetration. at this point I am getting about 155fps out of my bow with this setup, if I drop the weight a little and gain more Momentum I should also gain KE and therefor more penetration.

We will see what happens. I will keep you guys posted when I get the new test shafts.

TBRA

TheBigRedArcher · February 16, 2010, 10:32:00 PM

Ok. So here's what I came up with. both arrows are cx heritage 250's.

(original arrows)
681gr. @ 155fps = 36.34KE foot pounds w/ 16.1% foc (per bowjackson.com calculations)

(lighter combo)
580gr. @ 170fps = 37.23KE foot pounds w/ 11.6% foc (per bowjackson.com calculations)

I can add weight to the arrow by using weight tubes but I will drop speed and therefore KE.

TBRA

DesertDude · February 16, 2010, 10:53:00 PM

Hey Red I'm going to take a stab at this.....

What spine, point weight, and shaft lenght gives you the best results?

What are your goals from your equiptment?

What type of game are you going to hunt?

TheBigRedArcher · February 17, 2010, 10:41:00 AM

Dude:

Carbon express heritage 250 shafts, spine deflection of .373 which by the conversion chart I found on rosecityarchery.com is about a 70ish # spine. 29 3/4" shaft. and now a 200ish grain head.

Goals, good old fassion heavy but kicking kenetic energy on a not too fast but not too slow arrow.

Game, Anything that moves, I (being 6'4" 300lb individual) can get close enought to too shoot, and am willing to eat (read as NO SKUNKS) But mainly HOGS.

TBRA