Weak Spine Arrows With New Bow

[Grumpyfoot]

Let me start with what I'm working with.

I just got a new Bear Super Grizzly, 50# @ 28.

I took an average of my actual draw weight and it comes out to 54 pounds. I don't think my draw length is much over 28". When I measure it it comes to 28 3/4. That's beside the point I think.

I'm shooting a Black Eagle Vintage 350 spine with the aluminum insert that came with them. Cut to 30 1/2" long; 150 grain point; 3x4" feathers.

I shoot split finger, with a glove.

The spine calculator says the arrow should be under spined by around 5#.

When I shoot the arrows they fly very weak spined (nock left). I don't want to cut the arrows anymore, they are only hanging past the back of the bow 1/2" at full draw. I practice quite a bit, and have been working form and release alot lately. Yes I am holding the bow vertical, and have about 75 to 100 arrows through the bow.

Am I missing something? Is there something in my release I might be doing wrong? I haven't tried 300 spine arrows, and as bad as the arrow is flying, I don't think a 125 or 100 grain point will help.

I have tuned my Ben Pearson Colt, so I know I'm doing something right, and I really don't want to go under a 150 grain point on the Bear, as it is going to be my hunting bow.

Thanks for any advice.

P.S. I am shooting at 10 yards

[Orion]

Hmmmm.  I don't use the spine calculator, but a 350 spine arrow is about 89-90#@28 inches.  It looks to me like you're overspined, and the shaft is bouncing off the side plate, which would cause it to enter the target nock left at 10yards.  It's called a false weak reading. 

Something else seems a little out of whack.  You say your draw is 28 3/4, but also indicate your 30 1/2-inch arrow is only a half inch beyond the back of the bow at full draw, which would indicate a 30-inch draw.  Or is that after cutting down the 30 1/2-inch arrow?

Regardless, if you do have a 30-inch draw, which would require more spine than a 28 3/4-inch draw, I still think you would be overspined.  Would probably need another 100-150 grains up front to get the arrows flying straight.  For what it's worth, if your draw is about 28 3/4, I think you're closer to needing a 500 spine arrow if you want to stay with 150 grains up front. 

[Grumpyfoot]

Orion, I am not really sure how to measure my draw length on a trad bow. I do know that a 30 1/2" arrow does hang 1/2" in front of the back of the bow at full draw, so if that is a 30" draw length, thank you for clearing that up for me.

On the point of over spined, you saying that brings to my attention that I noticed on the side plate, there is a slight ware mark that looks like the arrow is rubbing it. Way over spined might be it. I was thinking it was because the arrow was too under spined. It does make sense a stiff arrow would come off the string to the right, rubbing the side plate.

Thank you for the insight, at least now I have a direction to move in.

[McDave]

Your draw length and the actual bow weight at your draw length are both more significant factors in choosing arrow spine than whatever weight is marked on the bow.  The longer the arrow, the stiffer the spine needed, and the more the actual draw weight, the stiffer the spine needed also.

It is not difficult to measure draw length on a trad bow.  The simplest way, if you have some help, is to have someone put a mark with a magic marker on the arrow where it crosses the back of the bow while you are at full draw.  Do that several times and find the midpoint of the marks (hopefully they're not too far apart).  If you don't have someone to help you, you can cut a piece of cardboard into a 2” square and put a hole in the middle that fits snugly onto the arrow, so it stays put when you move it up and down the arrow.  Put it on the arrow a little closer that you think your draw length is, draw the bow, and mark the spot where the cardboard ends up.  Do that several times and average the distances.

Draw length is measured from the valley of the arrow nock (the deepest part of the nock) to the marks you made on the arrow.  This isn't exact, but it's close enough for our purposes here.  Arrow length is measured from the valley of the nock to the base of the point.  The length of the point is not included in arrow length.

[Grumpyfoot]

I appreciate it McDave. I was always confused about whether draw length was measured to the low point in the grip, or the back of the bow. Now I know.

This measurement means my draw length is 30".

Thanks again

[McDave]

Brace height is measured from the string to the low point in the grip.

[Wheels2]

The Grizzly is not a real high performance bow so I doubt that you are under spined.  The Super Grizz is better performing than the standard. Have you tried a bare shaft?  Place some wraps of tape in the area of the fletching to mimick the weight of the fletching.  About 12 grains for your fletching.  Otherwise you will get a slightly weak reading with just the bare shaft.  +/- 2# difference in dynamic spine.
I like the method listed, using a piece of cardboard or an index card to measure true draw.  You can also set up your phone to video you draw.  Focusing on the front of the bow as seen from the side.

[Grumpyfoot]

Yeah, my brace height is good. When I shot compounds I always measured by the wing span method, and it always came out 28.5" to 28.75", that's why I assumed I measured from the deep spot of the grip because that's about 28".I thought this because I've heard shooting traditional would most likely make draw length shorter.

I've been curious about the AMO adding 1.75. I wasn't sure if that's just for the bow draw length, or for the archer too.

[Grumpyfoot]

Wheels, I have a draw length arrow, and I have used my phone to verify my dear length.

I have done bare shafting. I weighed all the components ;insert, feathers, nock, point, and total arrow weight. I do put tape on the back of the shaft to cover feather weight. Bare shafts fly almost completely sideways. Then I put fletching on the arrow to see if maybe I would see something I was doing wrong. Same thing, at 10 yards, arrow flies completely sideways to the target.

That said, I agree I think it's bouncing off of the side plate.

[McDave]

Yeah, my brace height is good. When I shot compounds I always measured by the wing span method, and it always came out 28.5" to 28.75", that's why I assumed I measured from the deep spot of the grip because that's about 28".I thought this because I've heard shooting traditional would most likely make draw length shorter.

I've been curious about the AMO adding 1.75. I wasn't sure if that's just for the bow draw length, or for the archer too.

Based on what you said above, I suspect that you are hauling back with your biceps rather than using your back muscles.  If you have strong biceps, you can haul the arrow back to your ear and beyond, but lose accuracy in the process.  The wing span method of measuring draw length is only an approximation, but it shouldn't be that far off.  Using your back muscles, you have an automatic door stop that keeps you from drawing back any further than your actual draw length.

BTW, the reason AMO adds 1.75” is because that is the average distance between the pressure point of the arrow on the strike plate and the back of most bows.  I'll bet Bear risers are pretty close to that, so you shouldn't be far off actual draw length by measuring to the back of the riser.

[Orion]

Re draw length.  McDave's description of measuring to the back of the bow is one way of doing it.  Using the AMO measurement, i.e., measuring to the throat of the grip and adding 1.75 inches, an arbitrary measure of the riser thickness, yield the same results to within a quarter of an inch or so.  Not enough to worry about.

But, as I suggested earlier, I think your shafts are too stiff, even at a 30-inch draw length. If your bow is 50#@28, it's in the neighborhood of 55#@30.  And you're shooting a relatively light front end. If you have any heavy inserts/and or heavier points, try to put about 300 grains up front and see what happens.  I'm pretty sure it will confirm my assessment.  Or, if you have some 500 spined shafts, or can borrow a few from a friend, give them a try with 150 grains up front.  Given your long draw, you may need to go with 400s, but I'd give 500s a try first. Good luck.

[Grumpyfoot]

I don't believe I'm using my bicep to draw, my arm doesn't get tired after 75 arrows or so, and I'm not that strong, average at beat. I do hit the natural wall you're speaking of, and pay close attention to back tension on release.

I have shot 2117 aluminum (400 spine) arrows with the 150's and it flies hard left too.

I have a field point test kit, and after work I'm going to start moving up in weight, and see what happens.

Looking at slow mo videos I've been taking, I believe you are both right. I think the arrow is bouncing off of the striker plate. The sideways flight is so drastic and exaggerated. Other bows I've tuned showed soft spine while tuning, but the flight was not so extreme, and the fletching would correct it well before reaching the target. These bare shaft hit the target almost completely sideways, and with fletching, they don't start to correct until a few feet in front of the target from 12 to 13 yards.

[Grumpyfoot]

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These are pictures of me at full draw with my 40# Ben Pearson Colt, and of my draw length arrow on my Ben Pearson BP-H90 47#, at full draw, up close.

I was bare shaft tuning the arrows for the Colt when this photo was taken.

[Wudstix]

I'm probably not going to be much help with carbon arrows, but if you can convert from woodies spine that I would think works for 55-56# recurve.  I would start with bow weight then add 5-7# for arrow over 28", and 5# for point weight (150).  Bow is of average performance, but if you have FF string, perhaps add another 5# of spine.  This would put you in the 65-69-74# spine range.  Whatever that converts to in the make and model of carbon you're shooting might get you headed in the right direction.
 

[Grumpyfoot]

Appreciate the tip Michal, I plan on looking in to converting the spines. Maybe I should give woodies a try, never used them before.

[Wudstix]

I might add this info is based on tapered shafts, it make a slight difference IMVHO.  I have found that my arrows can be a bit higher in spine and still shoot very well.  This allows me to get some more arrow weight.  My bows are all heavier than what you have, so possibly back down 5# in spine.  I've been shooting 60#+ since high school, so this is what my experience has shown me.
 

[Flbowhunter]

One  thing I have learned (over and over again) is that it is almost always cheaper to buy a test kit before you buy a full dozen arrows at least when setting up a new bow. That way you have some options that will get you closest to the arrow setup you want. I would suggest getting one that has one shaft that is weaker than you think will work, one that is stiffer, and one you think will be dead on.
As a note I agree with everyone above that you are likely getting a false weak. I’m shooting roughly the same poundage on 3 different bows (52-54) and a black eagle 340 with about 225 up front tunes to all of them in the 32.75-33” range.

[Kelly]

In the top picture how long is that arrow?

Ones true draw can not be measured when drawing a bow just for the sake of measuring. Your true draw is that when concentrating totally at shooting, then having someone watching you to see how much arrow is sticking out from the back of bow. It’s almost always shorter than the archer thinks.

[pdk25]

I am betting that those arrows are too stiff.  Really easy to find out if you can get ahold of some 400 spine arrows.  I think there is zero chance that you need 300 spine arrows.  If you swing by Lake Roberts NM, I have plenty that you could try, lol. 

[Grumpyfoot]

The arrow in the top picture is a Black Eagle Vintage full length 34". I was tuning that arrow for that bow. I do have some 500 spine arrows, I worked with a little last night, They were flying weak with 150's. I've got some Autumn Orange 2117 (400 spine) full length, bare shafts I'm going to start working with this evening.

I'm working 7/12's right now, it's hard to find enough time to fully tune in one session, so I'm doing a little at a time every day.

On the point about measuring while shooting, I'm going to measure and mark an arrow to measure the length while I'm shooting. That is a very good point.

Patrick, thank you for the offer, and if I lived near you I would take you up on it. I'm on the coast in Southeast Texas.