How much does grain weight affect trajectory

[fulldraw71]

I’ve been shooting 340 spine 100 gr tipped arrows out of my 61-62 lb bow. They weigh 412 grains each. I use my Last Chance scale to weigh things. I just built up some 300 spine with 4 fletch and 125 grain tips. These arrows weigh 465 grains each. I decided to see how these new arrows shot out of the same bow. Now disclaimer I have some coffee jitters this morning so it’s tough to have any accurate tests. The arrows flew straight and very nice. Very impressed with this 4 fletch configuration using 4 Q2i fusion Xll vanes in 2.1”. I said I had coffee tremors which is typical when I start shioting in the am until it wears out of my system but there were a few shots that felt great and I’m confident they were pretty good shots. All shots were at 30 yds. The shots I felt good with hit pretty much like my lighter arrows. I would have expected more drop with 55 more grains? Does that increase make that much of a difference in trajectory?

 

[big44a4]

I’ve been shooting 340 spine 100 gr tipped arrows out of my 61-62 lb bow. They weigh 412 grains each. I use my Last Chance scale to weigh things. I just built up some 300 spine with 4 fletch and 125 grain tips. These arrows weigh 465 grains each. I decided to see how these new arrows shot out of the same bow. Now disclaimer I have some coffee jitters this morning so it’s tough to have any accurate tests. The arrows flew straight and very nice. Very impressed with this 4 fletch configuration using 4 Q2i fusion Xll vanes in 2.1”. I said I had coffee tremors which is typical when I start shioting in the am until it wears out of my system but there were a few shots that felt great and I’m confident they were pretty good shots. All shots were at 30 yds. The shots I felt good with hit pretty much like my lighter arrows. I would have expected more drop with 55 more grains? Does that increase make that much of a difference in trajectory?

Not until further distances. My TAC arrows 375gr vs hunting 500gr fly nearly the same 20-40.

 

[nphunter]

You won't see much difference at close range at all. Your tune also makes a difference, I dropped 50gr and ended up using a sight tape like 3 or 4 sizes faster in the end. When I first built the arrows my new arrows 443gr vs my old 490gr arrows all grouped close at 80.
After swapping and tuning for the 443gr arrows, a lighter spine arrow and a smaller diameter arrow, they shot high with my sight tape. I think the .5mm difference in arrow size had them coming out slightly tail high, making them drop more at long range, which is why they still hit with the heavier arrow.

 

[fulldraw71]

Not until further distances. My TAC arrows 375gr vs hunting 500gr fly nearly the same 20-40.

That’s interesting info.

 

[fulldraw71]

You won't see much difference at close range at all. Your tune also makes a difference, I dropped 50gr and ended up using a sight tape like 3 or 4 sizes faster in the end. When I first built the arrows my new arrows 443gr vs my old 490gr arrows all grouped close at 80.
After swapping and tuning for the 443gr arrows, a lighter spine arrow and a smaller diameter arrow, they shot high with my sight tape. I think the .5mm difference in arrow size had them coming out slightly tail high, making them drop more at long range, which is why they still hit with the heavier arrow.

This is all interesting. Does this mean that your average Archer, who shoots 3-D and hunts, doesn’t mess with his bow sight very much if you’re only going 50 to 70 grains difference, but keeping the same diameter arrow?

 

[nphunter]

This is all interesting. Does this mean that your average Archer, who shoots 3-D and hunts, doesn’t mess with his bow sight very much if you’re only going 50 to 70 grains difference, but keeping the same diameter arrow?

It depends on how good of an archer and what they group like to start with. If a person is shooting 60+ yards regularly they will most likely notice a difference. If you shoot 3D for the score, you will surely notice a difference at the end of the day on your score sheet.

I shoot the same arrows for 3D and hunting, the advantage to going lighter is for better trajectory. It makes a difference in hunting and 3D, especially for non-marked yardage 3D or taking shots without a range finder. If you limit your shots to 20-40 you probably won't see a lot of difference.

I would say the average archer struggles enough with accuracy, I would suggest a bow is tuned for whichever arrow a person wants to shoot. For a hunter that should be the arrow they plan to hunt with tipped with the broadhead they plan to hunt with. Once that arrow is tuned leave the bow alone, if 3D arrows hit differently adjust the sight, put a different sight tape on or just learn the pin gap adjustments for the lighter arrows.

 

[dkime]

This is all interesting. Does this mean that your average Archer, who shoots 3-D and hunts, doesn’t mess with his bow sight very much if you’re only going 50 to 70 grains difference, but keeping the same diameter arrow?

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.

Speed junkies will claim speed saves trajectory and it’s easily refuted with a tiny bit of math or a 150$ rangefinder


Sent from my iPhone using Tapatalk

 

[fulldraw71]

Thanks for the info folks

 

[fulldraw71]

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

 

[180ls1]

You also may have added more drag (parachute effect) with the added fletches.

 

[fulldraw71]

You also may have added more drag (parachute effect) with the added fletches.

Good call! That is true and something I forgot to consider

 

[Beendare]

For a compound bow, hunter shooting critters at 40 yards, and in, there is very little disadvantage to shooting an arrow that is another 50 grains heavier.

The software programs and/or putting a heavier arrow in your bow set for the lighter arrow doesn’t give you the whole story. The best way to overlay the trajectories of a heavy/light arrow is to set your sight for the heavy arrow ( say 40y) then shoot both arrows. The lighter arrow- flatter trajectory will hit higher…but it aint much.

The tiny difference will amaze you, typically 1”-1 1/2” At 40y. It has to do with the orientation of sight vs rest. Putting a heavy arrow in a bow setup for lighter arrows starts that heavy arrow on a lower plane at a downward angle- skewing the real world difference.

 

[rearnakedchoke]

You probably won’t notice a difference within 40. All my hunting arrows are within 1gn. I’m dialed in with just standard nocks and when I put on the light knock that’s about 20gn I can’t tell a difference. This is considering the bow is paper tuned perfectly.

 

[Sled]

You probably won’t notice a difference within 40. All my hunting arrows are within 1gn. I’m dialed in with just standard nocks and when I put on the light knock that’s about 20gn I can’t tell a difference. This is considering the bow is paper tuned perfectly.

I've seen many setups react differently to changes in weight on an arrow. As someone said above, it's more often the tune and how forgiving it can be. If you're on the edge of your tune, softening the spine by adding weight to the front will show downrange. The same way adding weight to the back will stiffen. Changing the poundage of the bow can change the need to tune or spine of the shaft. Online calculators are helpful to get close in picking the right spine arrow and prevent small changes from becoming highly noticable downrange.

Edit: just noticed you said "can't" tell the difference. Looks like we agree.

 

[ShakeDown]

@thegoosano

 

[DanimalW]

Why did you go with a heavier arrow? Was it because of penetration issues or reading stuff on forums? I’ve been happy with 430-440 grain arrows with a 70 lb draw weight. Seems like a happy medium (for me) between trajectory and good penetration. My opinion is that shot placement is most important. I’m not taking a long shot unless conditions are perfect, and I don’t feel like a heavier arrow helps me in that situation. I’d rather have a little more room for error with trajectory. There are different trains of thought on this, and nobody is wrong if they’re making ethical shots and kills. So that’s why I asked why make the change? That answer might help provide better feedback.

 

[ResearchinStuff]

Did a little testing this winter, shooting a line from 60 yards and measuring vertical impact. 15 shots per arrow weight, threw out the highest and lowest impacts for each weight. For the remaining shots:

434 gr averaged 2.1" high
459 gr averaged 0.2" low
469 gr averaged 0.9" low

The bow grouped broadheads and field points together at 60 for all arrow weights. I elected to shoot the lightest option for reduced pin gaps, which makes a big difference for 40-60 yards shots for me. Ymmv.

 

[Mike Islander]

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.

 

[DanimalW]

Did a little testing this winter, shooting a line from 60 yards and measuring vertical impact. 15 shots per arrow weight, threw out the highest and lowest impacts for each weight. For the remaining shots:

434 gr averaged 2.1" high
459 gr averaged 0.2" low
469 gr averaged 0.9" low

The bow grouped broadheads and field points together at 60 for all arrow weights. I elected to shoot the lightest option for reduced pin gaps, which makes a big difference for 40-60 yards shots for me. Ymmv.

What’s your draw weight and bow?

 

[ResearchinStuff]

70#, 28.5", pse mach 1