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View Full Version : arrow spine/FOC...does it matter



HawgEnvy
03-19-2011, 05:40 PM
is it something I should worry about or is it over-rated? I shoot 3D for hunting practice only and only hunt deer and small game. both bows in my sig have 60# limbs,28.5" draw. I'm shooting 400 spine arrows. I can go as short as 27". I've got tight groups as it is w both 100 and 125gr heads w Blazer vanes.

also,is being over-spined an issue. I know under-spined will cause erratic arrow flight.

Hutch~n~Son Archery
03-19-2011, 05:53 PM
is it something I should worry about or is it over-rated? I shoot 3D for hunting practice only and only hunt deer and small game. both bows in my sig have 60# limbs,28.5" draw. I'm shooting 400 spine arrows. I can go as short as 27". I've got tight groups as it is w both 100 and 125gr heads w Blazer vanes.

also,is being over-spined an issue. I know under-spined will cause erratic arrow flight.

First, over spined is not an issue. But under spined is like a dry fire. That's if it is too under spined. FOC is not that much of an issue if you are a target shooter. As for a hunter it is a good thing to be close or above the % recommended. This is for penetration and flight.

HUTCH:cool:

NuttyNative
03-19-2011, 06:48 PM
As for a hunter it is a good thing to be close or above the % recommended. This is for penetration and flight.

HUTCH:cool:

Not to hijack here, what is FOC? And why is it a good thing for hunting? What's the formula to find it?

MLN1963
03-19-2011, 07:27 PM
Forward Of Center of the arrow. Basically it needs to balance right to fly right. Check out the link near the bottom of the page.

http://www.huntersfriend.com/carbon_arrows/hunting_arrows_selection_guide_chapter_4.htm

HawgEnvy
03-19-2011, 07:30 PM
FOC=Front of Center. It the balance point of the arrow with the broadhead/field point attached. Not exactly sure of the formula, but here goes. If I'm wrong,someone correct me. Find the balance point of the arrow by placing it on a sharp edge. Imagine your arrow balancing on a triangle. Mark the balance point. Insert the broadhead/FP then do it again. Since weight has been added to the front of the arrow, the balance point is now Front of Center(mark location,measure) To find the balance point,measure the arrow and divide it by 2.(ex.28"arrow divided by 2=14"center) that will give a ballpark figure. It may or may not be exact depending on your particular arrow(vanes,dipped,nocks,etc). If your balance point w BH is 12" from the end and the balance point w/o is 14", take 12 and divide by 14. It comes to .857(8%). IIRC,7-10% FOC is what we're going for.

like I said though, I could be wrong on this whole thing. It's new to me also. Hopefully the real pros will chime in.

NuttyNative
03-19-2011, 07:40 PM
Forward Of Center of the arrow. Basically it needs to balance right to fly right. Check out the link near the bottom of the page.

http://www.huntersfriend.com/carbon_arrows/hunting_arrows_selection_guide_chapter_4.htm

Excellent info, thanks a bunch. According to their chart with 100 gr tips I'm at 11.7% and with 125 it goes to 13.8%.

Hutch~n~Son Archery
03-19-2011, 11:21 PM
Maybe this can help. Take a simple dart used in a dart game. Okay most of the weight of the dart, is to the front of the body. When thrown the weight is what pulls the dart to its destination. If you lessened the weight, the dart would fly erratically. Reason the weight of the rear would almost equal the front. Thus the rear would catch up to the front and the dart has no stability. The arrow is the same principle. The weight needs to be closer to the front, in order to keep the arrow on the correct path.

Hutch:cool:

SonnyThomas
03-20-2011, 04:13 AM
So many arrows on the market, you have to look at the quality or I should say the make up of the arrow as weight is not a true indicator, such as Carbon Express's Rebels. Other arrows can have incredible spine, but can be to light, such as High Country's Pro Max.

Offhand, your set up with 400 spine arrows should be well and good. This would especially be true if your bow is launching the arrow true and spine checked and fletched your arrows according. Cutting your arrows shorter than 28" is probably unnecessary. I might have concern with the 125 gr heads, but good accuracy and good grouping is the real indicator here.

Hunting wise, I don't care for arrows going below 350 grs, but then I know some who have lighter arrows and get the job done. I'd say good arrow placement is helping get the job done.

NuttyNative
03-20-2011, 08:49 AM
I shoot the 340 Easton Axis nano tubes. 29.5" and a total weight of 430gr using 100 gr tips. Bow is at 68 pounds.

HawgEnvy
03-20-2011, 01:01 PM
I ordered some arrows from Harvest Time Archery. They're 400 spine. I think I'm going to stick w 100gr heads. They should be here tomorrow so I can get a feel for them. Has anyone else shot these?

Ehunter
03-21-2011, 04:17 AM
I personally like my arrows around 15% FOC or a little more. One thing that's come up recently though, arrows with a "Built-in" FOC. To me, these are a waste of money. Any decently made up arrow is going to have a decent FOC. Basically, the "weight forward" arrows have just been wrapped, or camo'ed at the front. Pick an arrow, add a point that is roughly 1/3 the weight of the shaft, and you'll be really close to that 10-15% that's recommended. As for spine, I do think you can be overspined, but it's pretty hard to do. It doesn't cause tuning problems for the most part, but a stiffer arrow is a heavier arrow. No reason to drop your speed when you can get the right spined arrows, or just slightly overspined.

RLW
03-21-2011, 04:41 AM
I shoot the 340 Easton Axis nano tubes. 29.5" and a total weight of 430gr using 100 gr tips. Bow is at 68 pounds.
I friend of mine shoots the same shaft, 28.75" with Blazers vanes and 100gr point.
We checked his F.O.C. on a couple arrows last month and they were 11.5 - 11.68%........I would imagine being a bit longer, yours are between to 11.0 -11.5%.
Vanes used will change FOC quite a bit, but looking at one of your previous posts, looks like you're using Blazers.
Think I also saw you're shooting a Pantera, with 30" draw length? Spine on those for your set-up is proably ok......"If" you use fixed blade broadheads and have some strange flight with them, like planning up high/right or left, might be slightly weak. So, "if" that happens, try backing off draw weight +/-3lbs and my guess is it cleans up.

Rockyhud
03-22-2011, 07:55 PM
I'm a true believer in high FOC. I found a very informative thread on AT that I also participated in where several posters exchanged info as to what arrows they built and how they performed. As you can see in my signature my arrows are a little over 17% FOC for my lighter Maximas and a little over 18% for my heavier Gold Tips. Here's the link on AT - http://www.archerytalk.com/vb/showthread.php?t=1097703&highlight=how+to+remove+glued+in+inserts.

There are also some very informative articles published by Dr Ed Ashby that are some of the best I've seen or read. He's studied arrows and broadheads for about 27 years and published numerous field test reports on arrow lethality. One of the aspects he covers, and very well I must say, is the affect that FOC has on penetration. You can find his entire collection of articles here - http://www.tradgang.com/ashby/.