Archery Talk Forum banner

1 - 20 of 33 Posts

·
Registered
Joined
·
21 Posts
Discussion Starter #1
Choosing the correct spine is so confusing. I've looked at charts that say I need a 330 spine and then used a shaft selector that said I needed a 550 spine. I have no idea anymore what to believe. So I'm reaching out to you! Help me understand, please!

Current Setup

Pearson Diesel
27" draw (shooting about a 28" Easton Epic ST 400 arrow - I know, not specific on length, but it's close)
Single Cam
60 lbs draw
75% letoff
100 grain G5 Montec
312 fps (giving 83.3 ft/lbs of kinetic energy which is plenty)

I'm not so concerned with speed of an arrow. I don't shoot long distances where I am and rarely have shots over 40 yards with my stand locations. I want to keep my kinetic energy up. I really like my current setup. However, it's time for a tune up on my bow so I'm getting new strings this spring and am looking at new arrows, too. Maybe the ones I have are right for me already? I bought these arrows when I bought the bow years ago before I knew what spine was!

Thanks for all of your help!
 

·
Born yank raised south
Joined
·
16,567 Posts
Choosing the correct spine is so confusing. I've looked at charts that say I need a 330 spine and then used a shaft selector that said I needed a 550 spine. I have no idea anymore what to believe. So I'm reaching out to you! Help me understand, please!

Current Setup

Pearson Diesel
27" draw (shooting about a 28" Easton Epic ST 400 arrow - I know, not specific on length, but it's close)
Single Cam
60 lbs draw
75% letoff
100 grain G5 Montec
312 fps (giving 83.3 ft/lbs of kinetic energy which is plenty)

I'm not so concerned with speed of an arrow. I don't shoot long distances where I am and rarely have shots over 40 yards with my stand locations. I want to keep my kinetic energy up. I really like my current setup. However, it's time for a tune up on my bow so I'm getting new strings this spring and am looking at new arrows, too. Maybe the ones I have are right for me already? I bought these arrows when I bought the bow years ago before I knew what spine was!

Thanks for all of your help!
You are probably borderline with you arrows cut to 28" on your spine. You can make those .400's work but the tuning might be a little more difficult. I think in the long run you would be better served with a .340/.350 spine as it should tune better overall, especially with fixed blade broad heads. Cutting your arrows back 1/2 to 1 inch would be better if you stick with the .400 spine.
 

·
Registered
Joined
·
2,552 Posts
so you are in that range 400 to 330 will work I have found that a slightly stiffer spine works better with broad heads, not really sure how you got 550 spine that's way weak. plus if you are shooting and grouping well then stick with the epics I shot them for years.
 

·
Registered
Joined
·
6,166 Posts
You defiantly don't need a 550..... If the .400 you shoot tune ok that tells you they are ok. I think a .330 is a little stiff at 28 inches and 60 lbs esspecially for a single cam. But Ive had less trouble tuning a stiff arrow over a weak arrow.

Either one would likely shoot just fine with a little tuning
Would need more specific info to check it on ot2 but off the top of my head niether a .400 or a .330 is completly out of the ballpark
 

·
Registered
Joined
·
6,166 Posts
so you are in that range 400 to 330 will work I have found that a slightly stiffer spine works better with broad heads, not really sure how you got 550 spine that's way weak. plus if you are shooting and grouping well then stick with the epics I shot them for years.
Had I read this first I would have just said "x2"
 

·
Registered
Joined
·
21 Posts
Discussion Starter #6
Thank you for the information.

What are some things that I would do that would make me change my spine? What if I go to a 125gr broad head? What if I use a heavier insert? What if I cut my shaft shorter or longer? I want to maximize my KE. I'm not a targer shooter and not a long distance shooter. I need something that will hit hard at <50 yards and be consistent.

I've been shooting bows for 15 years, but I've always just kind of been 'winging it' because I didn't realize for the longest time that there was so much to learn and I was the only person in my family to use a bow. I didn't really have anyone to teach me these things.
 

·
Registered
Joined
·
3,650 Posts
Thank you for the information.

What are some things that I would do that would make me change my spine? What if I go to a 125gr broad head? What if I use a heavier insert? What if I cut my shaft shorter or longer? I want to maximize my KE. I'm not a targer shooter and not a long distance shooter. I need something that will hit hard at <50 yards and be consistent.

I've been shooting bows for 15 years, but I've always just kind of been 'winging it' because I didn't realize for the longest time that there was so much to learn and I was the only person in my family to use a bow. I didn't really have anyone to teach me these things.
Yes if you start adding weight up front you will need to go up to a stiffer spine class from .400 to .350-.330 or whatever the brand you shoot has that is close. In my limited experience I've always gotten better results(consistent groups) from being overspined than slightly under.
 

·
Registered
Joined
·
1,692 Posts
Shooting 60 with a shorter draw length like you have a .400 should tune up great. If you had over a 28 inch draw then you would be better off with a .340 or something similar. That short of an arrow should give you added strength you need.
 

·
Registered
Joined
·
6,166 Posts
Things that weaken spine:

Added tip weight
Added length

Things that stiffen spine:

Added weight to the rear
Shorter arrow length

It's all incremental, how much you add or subtract determines how much the arrows characteristics change.
Foc is also important to consider, foc in the 12-20ish % range typically tunes easier and flies best. When you add weight to the back it lowers foc as is stiffens the spine.

If you want a real hard hitting arrow try a .300 with about 2-300 grains up front. Whatever it takes to even the spine out at the length you want
 

·
Registered
Joined
·
21 Posts
Discussion Starter #10
Things that weaken spine:

Added tip weight
Added length

Things that stiffen spine:

Added weight to the rear
Shorter arrow length

It's all incremental, how much you add or subtract determines how much the arrows characteristics change.
Foc is also important to consider, foc in the 12-20ish % range typically tunes easier and flies best. When you add weight to the back it lowers foc as is stiffens the spine.

If you want a real hard hitting arrow try a .300 with about 2-300 grains up front. Whatever it takes to even the spine out at the length you want
I've read a little about FOC, but can someone explain to me exactly what it is and how to measure it?
 

·
Registered
Joined
·
6,166 Posts
Foc is the % of the total arrow weight that is forward of center, since the light end always follows the heavy end higher foc helps with accuracy and penitration, think of it as tying a string to a baseball and throwing it. The baseball leads the string. If you get too much weight at the back (contrary to what nufletch try's to market). The back of the arrow is pushing the front to an extent. Leading to more erratic flight and less penitration


To figure out foc

Once your arrow is set up:
Divide the arrow's overall length (distance to the bottom of nock groove to end of shaft by 2).
Find the balance point. ...
Subtract center of the arrow measurement (calculated in step 1) from the balance point (calculated in step 2).
Multiply the resulting number in Step 3 by 100.


Some guys like as much as 20-25% plus
10-12% is largely reguarded as a minimum
I like to be around 14-15% with my hunting setup
 

·
Bowhunt/Homebrew have FUN
Joined
·
23,274 Posts
You are probably borderline with you arrows cut to 28" on your spine. You can make those .400's work but the tuning might be a little more difficult. I think in the long run you would be better served with a .340/.350 spine as it should tune better overall, especially with fixed blade broad heads. Cutting your arrows back 1/2 to 1 inch would be better if you stick with the .400 spine.
Perfect advice here....

Joe
 

·
Born yank raised south
Joined
·
16,567 Posts
Thank you for the information.

What are some things that I would do that would make me change my spine? What if I go to a 125gr broad head? What if I use a heavier insert? What if I cut my shaft shorter or longer? I want to maximize my KE. I'm not a targer shooter and not a long distance shooter. I need something that will hit hard at <50 yards and be consistent.

I've been shooting bows for 15 years, but I've always just kind of been 'winging it' because I didn't realize for the longest time that there was so much to learn and I was the only person in my family to use a bow. I didn't really have anyone to teach me these things.
If you are going to add weight up front I would suggest going to a heavier spine. Adding weight up front will soften or weaken the spine and with the .400's you are already borderline. If you want to add weight up front you would be best served with a .300 or .330/.340/.350 spine depending on how much weight you plan on adding....If you are just going to a 125 grain broad head then a .330/.340/.350 should suffice. If you plan on going with much more than 25 additional grains up front you would be best served with a .300. Adding weight up front creates higher Front of Center and moves your balance point forward. FOC is typically is known to increase your penetration, correct your arrow flight faster, and reduce your crosswind drift on windy days. Hope this helps brother!
 

·
Registered
Joined
·
6,166 Posts
The foc thing I posted was copied and pasted and doesn't make any sense.

How I figure it is take the over all arrow lenth and divide by 2= center of the shaft
Then find the balance point
Subtract the center number from the balance point and then divide that number into the total arrow lenth


For example say my hunting arrows are 29.5 inches long and my balance point is at 19 inches from the back of the arrow

So my center is 14.75
My balance point is 19 (balance point is the spot where you can set the arrow on your finger or some kind of folcrum and it will sit level)

19- 14.75= 4.25
4.25/29.5= .1440678

Therefore my foc would be about 14%
 

·
Registered
Joined
·
21 Posts
Discussion Starter #15
The foc thing I posted was copied and pasted and doesn't make any sense.

How I figure it is take the over all arrow lenth and divide by 2= center of the shaft
Then find the balance point
Subtract the center number from the balance point and then divide that number into the total arrow lenth


For example say my hunting arrows are 29.5 inches long and my balance point is at 19 inches from the back of the arrow

So my center is 14.75
My balance point is 19 (balance point is the spot where you can set the arrow on your finger or some kind of folcrum and it will sit level)

19- 14.75= 4.25
4.25/29.5= .1440678

Therefore my foc would be about 14%
I'm a scientist. This makes me happy. This is my language! :wink:
 

·
Registered
Joined
·
21 Posts
Discussion Starter #16
So I measured my arrows tonight for accuracy. They're 27 1/4". I didn't get a chance to measure my foc, though. That being said, I should be okay with keeping the 400 spine arrows, right? I am not really looking for a reason to change as I like my current setup. But more importantly I do want a correct setup.
 

·
Registered
Joined
·
1,692 Posts
Well how do you shoot with your current setup?? If they tuned up nicely with your bow then keep using them. Nothing wrong with shooting 400's with a 60# bow and a 27" dl.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #18
I think that a shoot and group pretty well up to 60 yards. But that doesn't mean I can't be better with a more preferable setup.
 

·
Grumpy Old Man
Joined
·
26,812 Posts
With your arrow length at 27.25 and a 100 grain tip you should be fine spine wise.
Running your arrow specs with GT's calculator shows an arrow weight of approximately 383 grains with a 12.7% foc.

I say approximately because I made an assumption that you were using Blazer vanes.
 

·
Registered
Joined
·
21 Posts
Discussion Starter #20
With your arrow length at 27.25 and a 100 grain tip you should be fine spine wise.
Running your arrow specs with GT's calculator shows an arrow weight of approximately 383 grains with a 12.7% foc.

I say approximately because I made an assumption that you were using Blazer vanes.
When I put my arrow on the scale a few nights ago - 385 grains. So the GT calculator is spot on!

With a FOC of 12.7%, do I need to add a little weight to the front (maybe a heavier insert?) to get that number up a little? I remember reading earlier in this thread that 10-12 was a minimum.
 
1 - 20 of 33 Posts
Top