Understanding arrows

[jnini21]

Someone told me the other day that my arrows had to weak of a spine for my set up. I don't completely understand what this means. I shoot a Mathews creed with a 28 1/2 inch draw and I'm pulling 67 pounds. I'm shooting FMJ 400 arrows. Are these arrows not the proper ones for my set up? Thanks

[dustoffer]

What "spine" refers to is the relative stiffness of the arrow based on a standardized test the industry uses. They used to place the shaft on two supports a fixed distance apart, and hang a standard weight at the middle of the shaft--the amount of deflection is the number they use to categorize the shafts. I would bet you might just be a bit weak on spine if you are shooting heavier broadheads. With 100gr, might be OK, if your shafts are cut to the minimum length to give clearance when at full draw/anchored.

[Dusty Britches]

Relation of spine - the amout of wiggle the rod has. Wiggle is the Archers Paradox - it moves up and down and side to side as it flies.

When a shorter arrow is shot from a low poundage bow, it can get by with a weaker spine becuase it doesn't have as much force pushing it. That way, short DL and low DW can shoot lighter arrows and still get efficient shots.

As DL and DW increase, the stiffness needs to increase to minimize archer's paradox. To make it stiffer, the arrow gets heavier, which really isn't significant becuase the stiffness keeps the arrow efficient.

Another way to think of it - Unwrap just the tip of the paper over a straw and blow it across the table to your friend's face. Watch how the paper tubing weakens as it nears the face. Now, lightly toss the straw the same distance. Watch what it does. Then, chunk it like a rock and watch what it does.

You now see the difference of under, correct, and over spined arrows.

So, yes, you may be underspined and might get a much more efficient flight with 340's. Maybe. See, your point weight, fletching, cresting/ wraps, nock also factor into spine. For the best bet, go to Easton Archery's web site and use their arrow shaft selection tool.

[jnini21]

So do they arrow sizes refer to the spine number? For instance since I shoot FMJ 400's then does the 400 refer to the stiffness. Is the higher the number the less stiff the arrow?

[Dave_S]

ttt

[txfireguy2003]

Yes, the numbers correspond with spine. On another note, depending on the length of your arrows, point weight etc as mentioned, i think the 400 is about right. I shot 400 spines out of my 67lb/28" black ice and they were prefect. That's with a 27" arrow and 100gr head.

[Outlaw_6]

So do they arrow sizes refer to the spine number? For instance since I shoot FMJ 400's then does the 400 refer to the stiffness. Is the higher the number the less stiff the arrow?

Yes, the higher the spine the less stiff the arrow. Basically, a .400 arrow flexes .4" with a 2 lb weight, a .500 arrow flexes .5" and a .340 .34".

I agree a .340 arrow would work better for you. How well do your arrows fly? How tight are your groups? Broadheads hitting with field points?

If you are not satified with the flight of your arrow flight, try decreasing your draw weight. If your arrow flight improves, then you would likely benefit from stiffer arrows if you want to continue shooting at the higher draw weight.

[wdixon]

It's hard to say because each bow is different in theory and by charts you are good, but we have a bowtech specialist at 60 lbs 28" draw and shoot a 500 spline with 120 grain tip at
29" paper tunes perfect, then we have a bowtech 101st 60 lbs 28" draw and it took a 340 spline with a 100 grain tip at 29" to paper tune properly. If you change tip weight you will change spline lighter = stiffer, so you can make small adjustments that way also. If you are right handed an arrow that is to stiff will hit left and one that is weak will hit right(opposite if you are a lefty)

[Bill]

Here's a really good source of information about arrow spine, and how it affects an arrow's flight, plus how to tune the bow. The info about adjusting berger buttons is not relevant to most compound bows, but this is written for all bows including string bows with those rests.

http://www.eastonarchery.com/img/downloads/software/tuning_guide.pdf

How does your bow shoot at 20 yards if you shoot 3 arrows with field points, and then shoot them again with broadheads? That's the final test.

[Ttechhunter]

What is the length of your arrows? I shot a creed at 27.5" draw 67 lbs shooting a 28" arrow (fmj 400 spine) and they flew great. Decrease the draw weight instead of buying new arrows if you want to save money.