How much does grain weight affect trajectory

[BoilerBowHunter]

No, total drop will be affected beyond 40 but the drop per yard is going to be similar across arrow weights and speeds from 400-500gr.

Trajectory is a curve, you get to look at a small portion of that curve when looking through your sight. As you go heavier the portion of the curve you get to look at is shifted down but the section of the curve remains very stable.

407gr shaft going 300= 1.9” drop per yard at 50
475gr going 290 = 2.4” drop per yard at 50
515 going 270 = 2.6” drop per yard at 50.

Extreme spread of .7” inches when you have the pins or sight tape adjusted correctly for an apples to apples comparison.

@dkime

I was researching this and came across this thread. Can you share how you calculated your drop numbers? Is there a basic formula you are using, or do you have some sort of software that's doing it? I have toyed with building a slightly lighter arrow (say going from 525gr down to 475gr), but I'm not convinced it's worth it if the trajectory impacts are this minimal.

 

[Idaboy]

Theoretically weight makes no difference...at identical shape and speed.

So if weight added doesn't change arrow shape, velocity is your controlling factor. Since a heavier arrow changes velocity if you don't change your draw weight, that's what causes the additional drop at longer distance.

^^^ this....depending on your bow force at moment of release it has to overcome more mass, so heavy arrow will be ever so slightly slower at immediate exit velocity. After that if in a vacuum, they would then drop at same rate. Small grain changes probably will only notice a few FPS speed.
.... In real world, non vacuum conditions, you then have air resistance/drag that will slow speed and thus more drop. A heavy arrow will have more momentum to overcome the drag (eg think of throwing a baseball vs a whiffle ball). I went up 60gr on my BH from 420 to 480 for FOC and insert system and noted very little POI difference

 

[dkime]

@dkime

I was researching this and came across this thread. Can you share how you calculated your drop numbers? Is there a basic formula you are using, or do you have some sort of software that's doing it? I have toyed with building a slightly lighter arrow (say going from 525gr down to 475gr), but I'm not convinced it's worth it if the trajectory impacts are this minimal.

I rely on archers advantage and softwares like this, it’s not a perfect formula in terms of how much each one will drop but it’s a good apples to apples comparison when you keep things the same in the software. The difference for me in real life testing comes at the 80yd mark. 515gr to 540gr is only about 8” of drop for my setup. Which equates to roughly 2yds of trajectory.

In your situation 525 to 475 it really just depends on how you’re cutting the weight. If the heavier shaft is more durable then I would go heavier. If it’s all point weight manipulation to get there I would just shoot the more accurate point weight (which ever gives you the least amount of horizontal dispersion)


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[BoilerBowHunter]

I rely on archers advantage and softwares like this, it’s not a perfect formula in terms of how much each one will drop but it’s a good apples to apples comparison when you keep things the same in the software. The difference for me in real life testing comes at the 80yd mark. 515gr to 540gr is only about 8” of drop for my setup. Which equates to roughly 2yds of trajectory.

In your situation 525 to 475 it really just depends on how you’re cutting the weight. If the heavier shaft is more durable then I would go heavier. If it’s all point weight manipulation to get there I would just shoot the more accurate point weight (which ever gives you the least amount of horizontal dispersion)

Thanks for the reply. The delta in my scenario would all be shaft weight. Going from a Black Eagle Rampage to a Sirius Apollo or RIP TKO with everything else staying consistent. I can’t say if it’s more durable or not. Realistically I don’t intend to shoot past ~50 yards, so it seems like any difference is negligible in terms of trajectory. I don’t want to give up the mass to not really gain anything in terms of trajectory.

 

[accountantsanonymous]

I rely on archers advantage and softwares like this, it’s not a perfect formula in terms of how much each one will drop but it’s a good apples to apples comparison when you keep things the same in the software. The difference for me in real life testing comes at the 80yd mark. 515gr to 540gr is only about 8” of drop for my setup. Which equates to roughly 2yds of trajectory.

In your situation 525 to 475 it really just depends on how you’re cutting the weight. If the heavier shaft is more durable then I would go heavier. If it’s all point weight manipulation to get there I would just shoot the more accurate point weight (which ever gives you the least amount of horizontal dispersion)


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Second vote for archers advantage or similar tool. Typically if you input all your parameters correctly, it’s pretty spot on.

 

[dkime]

Thanks for the reply. The delta in my scenario would all be shaft weight. Going from a Black Eagle Rampage to a Sirius Apollo or RIP TKO with everything else staying consistent. I can’t say if it’s more durable or not. Realistically I don’t intend to shoot past ~50 yards, so it seems like any difference is negligible in terms of trajectory. I don’t want to give up the mass to not really gain anything in terms of trajectory.

I can’t make any recommendations on any of those shafts, but inside of 50 and more realistically 40 there’s not much of a difference you’re going to experience. The heavy weight along with a non whistling broadhead and a properly designed vane (doesn’t exist but not on topic) is going to be your best option just from a the standpoint of quieting the whole system down. Bow, arrow flight, etc. You also haven’t mentioned your poundage but If I were in your hunting situation using my specs 29/70 525 would be the easy button


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[Beendare]

Well I’ll give an update. I got home today. I’m fresh. I’m a little more steady than I was this morning and I’m putting things to the test. I can say now for sure that at 20 yards the two arrows pretty much hit together. At 30 yards the heavier arrow is about 2 to 3 inches low. And at 40 yards the heavier arrow is about 5 to 6 inches low. So they’re definitely is a difference. These are not scientific measurements. This is me looking at the arrows in the target with my naked eye. And it is fairly breezy today with some occasional gusts. But I’m consistent in my shooting for the most part so I’m confident there is a noticeable difference. This is coming out of a 2012 Martin Onza 3 that IBOs between 335-345. So it’s not a slow bow. Anyways, now I know ha ha

Bad test protocal, You are skewing the test per your testing....starting the heavy arrow on a lower plane in relation to your sight- which is what really matters here.

Move your sight so that the heavier arrow is dead on at 40y, then shoot both. I bet the light arrow is maybe an inch higher. The Q for all of us, Is that enough to matter on a real animal?

Yes, the heavier arrow will show a significant difference at long 80y ranges...but at bowhunting distances on critters, its negligible.

EDIT; The Chart info posted by Dkime is accurate...but it's all about how you overlay those charts. Shooting the light arrow in a bow setup for the heavier arrow gives us more of a realistic overlay of real world trajectories.

 

[Tilzbow]

Bad test protocal, You are skewing the test per your testing....starting the heavy arrow on a lower plane in relation to your sight- which is what really matters here.

Move your sight so that the heavier arrow is dead on at 40y, then shoot both. I bet the light arrow is maybe an inch higher. The Q for all of us, Is that enough to matter on a real animal?

Yes, the heavier arrow will show a significant difference at long 80y ranges...but at bowhunting distances on critters, its negligible.

EDIT; The Chart info posted by Dkime is accurate...but it's all about how you overlay those charts. Shooting the light arrow in a bow setup for the heavier arrow gives us more of a realistic overlay of real world trajectories.

Why is the heavy arrow on a lower plane? Are you assuming the outside diameter is slightly larger since in OP’s example it’s a heavier spine version of the same shaft?

 

[Beendare]

Why is the heavy arrow on a lower plane? Are you assuming the outside diameter is slightly larger since in OP’s example it’s a heavier spine version of the same shaft?

No, if think it through.....its all about how you overlay trajectories and that is all about the relation of your sight to your rest. You lower your sight with the heavier arrow [less distance between the rest and sight]....which in effect raises your rest and puts the heavier arrow on a higher starting plane.


Shooting the heavy arrow with sight set for the light arrow starts the heavy arrow pointing lower right out of the bow.

It has the same trajectory- of course- but since it starts lower, it doesn't reflect real world of what you would experience when hunting with lighter vs heavier arrows. In real world, the difference is not much on shots 40y and in.

It's always better to put a light arrow in a bow set for the heavier arrow....doing it the other way exaggerates the difference.

Try it, you will see.

 

[Beendare]

I should add; I'm talking hunting shots.

One inch of difference really doesn't usually matter much on a hunt shot but to the 3D guys one inch can mean a higher score.
Edited for spelling

 

[Tilzbow]

Thanks for the explanation.