Bow-arrow math question

[robtattoo]

I've got a hunt coming up in July, going off to Namibia for a week.
My problem (if you can call it a problem) is deciding on my bow/arrow configuration.

I have several bows I can take, from 58# right on up to 76# I'm consistently accurate with both weight extremes.

I have a few different arrow options available too, but they all run at around 580-620gn I have arrows tuned to shoot well from all my draw-weights.

The thing I can't seem to get right in my head is that the lower weight bows are nearly as fast as the heavyweighs, shooting the same weight arrows (within 10fps)

Whenever I read of folks hunting Africa they always seem to be shooting huge bow-weights (70#+) and this has prompted this question

Given that accuracy isn't an issue (as I say, I can shoot them all equally) what would be the advantage of shooting the heavier bow?

[robtattoo]

Oh, incedentally, I'll be shooting razor sharp, 2,3 & 4 bladed heads that fly to perfection & penetrate like surgeons scalpels.

Just thought I'd get that one out of the way!  :D

[Bob Walker]

My redneck brother from across the pond!! Top of the morning to you. IF, you shoot the range of weights equally, then the heavier bows would give you a flatter trajectory and a faster "in flight" time which would decrease the chances of the animal "jumping the string". Just ask Barry Wensel about them wart hogs.
Hope you have a great time on your hunt. Any progress on the property over here yet?
Bob

[khardrunner]

If indeed the lighter bows shoot arrows of the same mass at the same velocity of the heavy bows, then it really doesn't matter which you take. Trajectory and momentum will be the same. 10fps may be worth taking the heavy bow though.

I would look into getting a more efficient heavy bow if $$ allows it. Perhaps getting one from the company who makes the lighter bow, which is obvioiusly very efficient.

[John Nail]

If I was in your enviable position, I'd go to the "dangerous game" forum and PM some of the folks who have been there. I'm sure you'd recieve some solid advice.
Good Luck over there, and post a bunch of pictures!

[tradtusker]

hey Rob.
hope you had a good christmass mate!
iv also been running different combos through my head for the hunt, but im pretty much set on my 58# shrew with arrows weighing 560grs to 580grs and am more than confident that will be plenty for all the game im wanting to take including Wildebeest and Gemsbok.
i might make some heavys up if i decide to take a big Eland, something in the 750gr range.

it is strange that the heavyer bows are not giving you much more speed than the lighter bows  :confused: , and with only 10fps gain there is no massive advantage shooting the heavy.

obviously if the heavyer bows could shoot a heavyer arrow the same speed they would be better, but by the sounds your bows missed there physics classe's   :D      

we'l have to catch up soon talk about the up and comming hunts and throw a few arrows around!

cheers Andy

[Rico]

Shoot a 750++ gr arrow out of both bows that would be the real test.

[njstykbow]

robtattoo,

Any of your bows will obviously work.  If you plug the numbers into a KE calculator, you'll find 10 fps makes a very considerable difference.  When I go in 2009, I'll be carrying the heaviest bow I can shoot accurately...which also shoots the fastest arrow (given the same gr/lb).  Best of luck on your adventure.

Joe

[njstykbow]

Here's an example of what I was referring to in the above post.

Arrow #1:  600 gr. @ 170 fps = 38.51 ft/lbs KE
Arrow #2:  600 gr. @ 180 fps = 43.18 ft/lbs KE

Five ft/lbs increase is huge for a traditional bow in relation to the relatively low numbers we're already dealing with.

Joe

[ChuckC]

There are two things that matter.  speed and weight of the projectile.  If both bows send the same projectile at the same speed, then it doesn't matter which one you use.  

As joe shows above, when looking at the KE end of things, speed matters a bunch.  But.  when looking at it in a Momentum equation, I believe speed is not as important a factor.  
ChuckC

[njstykbow]

ChuckC

Momentum goes from .45 on arrow #1 to .48 on arrow #2, also a pretty big jump.

[Dirty Bill]

I recommend razor sharp 2 blade heads. Send The 8th dwarf an e mail.  

[tradtusker]

if you ask Paul 8th dwarf he'l tell ya "shoot 135gr magnus"  

[ChuckC]

Thanks Joe.
ChuckC

[robtattoo]

:D  :D  I think I've got every broadhead BUT the 135 Magnus now! I was planning on using a mixture of 200gn (inc adapter) STOS & Zwickey Delta 2-bladers on the big stuff (Eland) & Woodsmen & Snuffers (200gn again) on the deer-sized stuff.
I've been aout & had a play this afternoon, with the 3 top contenders. 57@28 62" Horne Combo longbow, (Double carbon & bamboo) 52@27 52" Shrew Classic hunter (Actionboo) & my 60" Great Plains longbow 62@27 (maple limbs) I draw the lower poundage to 30" dead & the Plains to 29-1/2" The respective weights at my draws jump to 62 for the Horne, 62 for the Shrew & 70 for the Plains. Shooting the same weight arrows (the same arrows, actually!) there's virtually no discernable speed difference between the Horne & Plains bows, the Shrew is marginally, but noticeably slower. I'm kinda shocked by the efficiency difference between the 3 bows, length, material & limb design really do make one heck of a difference to performance (Yeah yeah, I know that y'all knew this)

[tradtusker]

dont think you can go wrong with the shrew out of the hides   :D   and the Horne for the stands and walk and stalk...ah    
at this point i recon im only gonna take 1 bow!

[LEOPARD]

Hi Rob, that's real weird that the speeds are so similar out of all the different weights using the same arrows!
Have you tried really heavy arrows, like 800grainers, in both and seen if that makes a difference? I'd be curious to see if it did! Another thing I was thinking of, and it would be a hard thing to measure accurately, is whether the arrows shot out of the heavier bows held their speed better than the arrows out of the lighter bows at longer distance i.e. 40-50 yards.

Nigel

[Glenn Newell]

I have found the same thing, I have a lighter bow that shoots very heavy arrows around 16 grains per pound almost the same as a much heavier bow. I don't bother with the heavy bow now. My hunting mate shoots a heavier bow than me but he uses lighter arrows and his results are nowhere near as good as mine. I get much better penetration and quicker kills than he does...Glenn...

[Sixby]

What you have going is a highly efficient lower weight bow and a mediochre heavy weight bow., When all things are equal the heavier bow should shoot an arrow x ammount of gpi the same speed that a lower weight bow shoots x ammount of gpi s, If your lower weight bow is shooting the same weight arrow approx the same speed the use it. Unless I'm wrong 10 fps = about 4 to 5 foot lbs energy. Unless you are going after the big 5 I wouldn't have a problem shooting antelope ect with a 58 lb bow that is efficient and moving a 580 gr arrow 175 to 180 fps. Maybe even a little less. Have a great hunt!!! Steve

[khardrunner]

How are you guys getting units of ft. lbs (and ft./lbs for that matter) for KE? I'm just a young physics nerd, but I can't get those units out of KE=1/2mv^2 no matter what units I use for each variable. I can get all sorts of stuff, but not simply foot pounds. That said, your translations of KE to arrow penetration are misleading. Please, feel free to correct me if I'm wrong...I love to see things from another point of view.

I prefer a simpler solution. Stick with momentum. It is a better predictor of penetration capability and an easier formula (p=mv). From what I've learned, foot pounds is a unit of force, not energy. These are two very different things in how they relate to arrow penetration and the ability of arrows to take big game.