Spine and High FOC question/suggestion

[IndaTimber]

I'm looking to add a little FOC, well a lot of FOC, and I'm hoping to get pointed in the right direction.  I'm going to be switching from wood to carbon as well, but have shot carbons in the past so I'm familiar with them.  Understanding that extra weight up front changes the dynamic spine, how much is actually changed or is it basically that the calculators change because of the extra weight? 

Currently I'm shooting a 58" Kanati 55# @ 28" (I draw 29").  I'd like to be around 25% FOC with puts me running close to 400 grains total on the front of a .340 spine gold tip velocity, but the calculator puts they dynamic spine of the at arrow at 34.5 (actually had to use the generic carbon 340 and put in the velocity weight in).  I first thought .340 would be stiff but now I'm confused, which isn't hard to do AT ALL!

For the guys that run high FOC setups, does this sound right?  I'm going to order some test arrows and I'm wondering what spine to start with.

As always thanks in advance.

[JohnV]

I would start with a 340 shaft, especially if your bow is cut past center.  I shoot 340 shafts with about 250 grains of tip weight out of my ACS longbows and they fly just fine with my 57# and 53# limbs.  I draw 28" and cut my shafts at 30".

[TomMcDonald]

Those calculators are crud in my experience.
Starting at .340 is probably a good idea.
I'm shooting a 50# r/d longbow cut a bit past centre.
Using full length .400 spine Easton carbons with 400 grains up front with a bit extra for aluminium footing and a 12 strand D97 string.
They were shooting weak till I built out the shelf with some Velcro and a matchstick. They are now perfect so .340 will be a good place to start for you.
There are lots of other variables that will make each individual's experience different though.
Cheers,
Tom.

[Pfranchise]

If your looking to put 400gr up front you are going to need a really stiff shaft. Im not sure you will be able to make that happen. I’m not sure a .340 will be stiff enough. I just put the combo in a calculator and a 30” arrow with 300gr up front spines at 50.9lb. A 30” .300 spine shaft with 300gr up front  comes in at 59.4lb. The .300 might be closer for you. The spine calculators are just meant to get you close they aren’t super accurate. Make sure you bare shaft tune when your working on that arrow setup. Lancaster sells single shafts if you wanted to buy a few different brands and spines to experiment with to find what works.

[Friend]

My personal Ultra EFOC arrow setups typically run from 15 to 20#s under spined.

Had discussed these findings with Stu many years ago. He was quite aware of this occurrence yet did not know how to incorporate into the equation.

By far, personally, the most solid bare shafting arrows I had ever shot. Have even shot 3D rounds with these bare shafts.

[IndaTimber]

Thanks for all the information. I’m going to order a couple .340’s and .300’s with different inserts and point weights and start bare shafting. I’ll report back but thanks again for the information.

[Bart S]

I've been shooting GT velocities for a few years now out of a 60# @ 29" Blacktail. Using 100 grain brass inserts and 200 grain heads, the .300 spine tuned easily for me, but are a bit longer than I prefer--31 1/4".

Despite being the most forgiving setup I've ever used, I've been toying with chopping them down a little and seeing how they fly with 250 grain heads.

[kenneth butler]

400 up front is a lot for 55 pounds. You are going to have a high arc. If that is what you want it will take a stiff shaft. With a 29" draw and shafts at least 30" you might well need a 300 spine. I will see if I can calculate it. >>>-----> Ken

[ozy clint]

Well after my recent experience building buffalo arrows I'm going to suggest along other lines.

In building a high FOC arrow you soon encounter diminishing returns with adding weight up front. It is very easy to end up with a very heavy arrow for a given setup.

The key IMO is to use a weaker than you think shaft and a long footing. I say weak because a weaker shaft will be lighter GPI. This is key. The back end will be lighter allowing to achieve desired FOC before the arrow becomes grossly heavy. The long footing, (perhaps up to 4-6") adds further mass and strength up front but also serves to stiffen the weak shaft sufficiently. The actual flexible portion of the arrow becomes shorter without trimming the total arrow length. Between trimming the shaft and varying the footing length you can tune it. Furthermore, if the footing is such that it gets drawn onto the shelf the extra diameter effectively builds out the side plate giving more stiffening effect to the 'weak' shaft.

I wouldn't be surprised if you could use a 500 spine, with long footing and get 30+% FOC and not be excessively heavy.

Note- the buff arrow I spoke of is an axis 400 at about 30". 5" footing, 640gr up front.  33.5% FOC. 70# bow.

[kenneth butler]

  Yes a footing is a much easier way to get that much weight up front with that long of a shaft. I should have mentioned  an alternate route but I was caught up in your spine question and  now see 300 spine won't even get you where you want to be.
  Looks like OZY has done the testing for you. >>>-----> Ken

[IndaTimber]

Thanks for all the information. I ended up with 480 up front, 200 insert, 125 adapter, and 155 BH. The insert is two brass inserts joined together, Samkowiak has a bideo on this. The 340’s bareshafted really well for me at 20 and that’s what I had the most confidence in. I feel that it is also more forgiving as well, contributing to my confidence. I’m sure I’ll learn more and adjust accordingly but I feel comfortable with this setup currently.

Thanks again, and Ozzy your information will prove valuable for many!

[kenneth butler]

If it is shooting well for you, that is all that matters. >>>>-----> Ken

[HartHeart]

My personal Ultra EFOC arrow setups typically run from 15 to 20#s under spined.

Had discussed these findings with Stu many years ago. He was quite aware of this occurrence yet did not know how to incorporate into the equation.

By far, personally, the most solid bare shafting arrows I had ever shot. Have even shot 3D rounds with these bare shafts.

Would you care to share some of your UEFOC builds?