Do I need to make adjustments to my Elk Arrow?

[CurlyTail]

Last Fall I shot my first archery Elk, a Spike, at 30 yards.

Perfect broadside angle, arrow went through (double lung) and stuck out the other side - hanging on by the fletchings. He went 60 yards and died leaving a decent bloodtrail, nothing massive.

Although pleased with the final result, I was somewhat surprised that I did not get a complete pass through. I was shooting a 100 grain 4 blade Magnus Stinger broadhead, on a VAP V1 arrow with the 95 grain stainless steel outsert, and a 20 grain nocturnal lighted nock. Total arrow weight was 270 grains. My bow is set at 63lbs, with a draw length of 29. ibs bow speed 330fps.

My goal is a complete pass through. Do you think I should adjust any components this off season. I was shooting nice groups with this setup, and the broadheads were grouping with my field points.

Do you think a complete pass through is that big a deal, I think I could work my bow up to 65-67lbs if needed. My initial thought was to just switch to a 2 blage Magnus Buzzcut and leave everything else the same. Any ideas or comments?

[olympushunt]

Total arrow weight was 270 grains. Any ideas or comments?

Total?? As in arrow with bhead and the whole ball of wax???? I think that is to light. I like to be above 400. Weight plays a huge factor in kinetic energy (KE) down the flight path. Light arrows will dissipate KE much quicker than an arrow with more mass. Think of a 55 grain .223 bullet compared to a 250 grain 30 cal bullet. At 400 yards the .223 is spent and the 30 cal bullet will still punch HARD. Kinetic energy is where you will get the pass through punch. Nice job on the spike! You may have clipped a rib and slowed that arrow a lot but you got him so that is what counts. I personally think you don't need to mess with bhead type or bow weight. Pass through shots are ideal but not the end of the world if you don't. I shoot Easton FMJ arrows that are like a bacon wrapped steak....mmmmmm steaaaaak. lol They are an aluminum wrapped carbon shaft. Great tolerances and great grains per inch. Just the shaft weight is over 300.
Just my .02

[Swede]

Curly, your arrow weight does not sound right to me. If you are shooting a 26 inch (short) arrow, 170 grains would be just a little over 6.5 gr. per inch including nock, insert and vanes.
I have shot 355 grain arrows and killed elk. I consider them too light, but have had a complete pass through up to 40 yards. Even if you have a 370 gr. arrow including the 100 gr. broadhead you can easily bring up the weight and KE by adding a full length strand of weed eater string down the shaft of your arrow. If you are truly 270 grains total, you might add two strands and a heavier broadhead to keep your FOC in the 10%-15% range. I would not think that would weaken the arrow spine significantly. A little testing would show you how your arrows are flying.
Note: One strand of weed eater string in the shaft of an arrow will rattle a little if you deliberately shake it. I have not noticed it to be any problem out in the field.

[CurlyTail]

oops. Edit that arrow weight to 470 grains total weight.

[Swede]

Curly, if your arrow flies true, I would leave it alone. It is plenty heavy and capable of killing anything with hooves and antlers.

[Swede]

Another thought occurred to me. Your comment on the adequate but not abundant blood trail caused me to remember; minimal blood trails happen on both deer and elk and is no reflection of broadhead quality or sharpness. Sometimes you get a great blood trail, but many times it is very light. I have noticed this most shooting from a tree stand. This occurs because the arrow goes in high and does not pass completely through.

[olympushunt]

oops. Edit that arrow weight to 470 grains total weight.

That makes way more sense. You have more than enough KE to pass all the way through an elk. You obviously know more from your autopsy but you may have nicked a rib? You have about a 50/50 chance and even a small amount of contact will rob your arrow of a lot of penetration. My suggestion...if you are ok with it is to shoot a bunch more elk, some 6 points, a 7x8, a few 5x5s and some smaller bulls too. Then you will find you are blowing through a fair portion of them.

[82ndreddevil]

That is very surprising that you didn't get complete pass through on your bull. The last two elk I got were at 45 yards broadside and both times they passed through like nothing. One arrow bounced off a tree and back towards me after going through him, the other chipped my broadheads on rocks after the pass through. My arrows weighed 400 grains and my bow is at 70 pounds. I can't see the 7 pound difference making that much difference, plus your arrow should have better penetration than mine. Very interesting.

[CurlyTail]

I was also surprised that I did not get a complete pass through. I tried to optimize my arrows to get that result.

I think shooting several more Bulls to get a larger sample size is a fantastic idea! I will work on that.

I can't recall noticing that the arrow hit bone, but it must have.

I shot a Bull with my muzzleloader once, and hit him high in the lungs. It took a full 90 seconds for this entire chest cavity to fill with blood before any spilled out the bullet hole. If that Elk had been running, it would have been quite a long distance before any blood trail would be visible. I remember this because I was frantically trying to reload (without being seen which is impossible) thinking I had somehow missed the shot as there was no visible reaction from the Bull and no blood stain see. Then he fell over dead much to my relief.

I am thinking of picking up an inexpensive chronograph to see my true arrow speed. I live in an area where there are no archery Pro shops so I am trying to learn to do things myself.

[Heartwood]

Curly,

Elknut did extensive real world penetration testing a number of years ago. SEE archerytalk thread. He found that 6.6 grains per pound of draw weight gave the best penetration into a uniform substrate. You are actually on the to heavy side for optimum penetration at 7.46 gr./#. At 63 # you would want an arrow around 416gr. + or- 5%. That said, you most certianly hit one or two ribs on your spike.

[Swede]

Elknut did extensive real world penetration testing a number of years ago. SEE archerytalk thread. He found that 6.6 grains per pound of draw weight gave the best penetration into a uniform substrate.

Without wanting to just be contentious, I must disagree here. Elknut did not prove that 6.6 gr./ lb. is optimal for penetration on anything. A lighter arrow in flight will not maintain its kinetic energy KE over a distance like a heavier arrow will. A 6.6 gr. / lb. arrow will not leave the bow with as much energy as a 7.5 gr. per lb. (roughly Curly's setup) arrow will, and at 40 yards the lighter arrow has lost far more energy than the heavier one. All things being equal, the arrow with the most KE will penetrate the most when it hits the mark.

[82ndreddevil]

Maybe there are just too many "X Factors" to account for to determine why the arrow did not pass through like expected. The numbers say it should have gone through, but the many unknown or inconsistent variables kept it from happening. If I remember correctly the Magnus Stingers are pretty large broadheads. Does anyone think that possibly broadheads with a lot of surface area create more resistance than perhaps a smaller one?

[olympushunt]

Elknut did extensive real world penetration testing a number of years ago. SEE archerytalk thread. He found that 6.6 grains per pound of draw weight gave the best penetration into a uniform substrate.

Without wanting to just be contentious, I must disagree here. Elknut did not prove that 6.6 gr./ lb. is optimal for penetration on anything. A lighter arrow in flight will not maintain its kinetic energy KE over a distance like a heavier arrow will. A 6.6 gr. / lb. arrow will not leave the bow with as much energy as a 7.5 gr. per lb. (roughly Curly's setup) arrow will, and at 40 yards the lighter arrow has lost far more energy than the heavier one. All things being equal, the arrow with the most KE will penetrate the most when it hits the mark.

Not to be even more contentious...lol....I don't necessarily agree with ya pops on the whole heavier (7.5gr/lb Vs the 6.6 gr/lb) arrow is always the better penetrator.
With just that statement alone we are ignoring some pretty important physics here. Back again to the .223 bullet (a flavorite coyote getter) an extremely light "arrow" that has A LOT more KE than my 450 grain arrow out of the gate. A lot! The KE formula is 1/2 x Mass x Velocity squared. Emphasis on the SQUARED part. Light weight stuff loses velocity (thus KE) much faster so down the road it becomes less effective than the heavier stuff. So at 30 yards....gimme the light fast zippity zip stuff. This is counter intuitive to what most folks think is beneficial. With light arrows our trajectory is flatter (to a point) and gives us more fudge room guessing longer distances. But if you don't have the mustard at the end why bother? So my whole point is....it is not fair to do comparisons on weight alone. We need to look at velocity as a huge factor.....a squared factor at that! Another common mistake is doing tests at a set range....say 20 yards or 30 yards. I have no idea what distance Elknut did the tests at but lets see the graph curve of penetration (or more accurately KE) at distances 20 through 80+. That is where some eyes will get opened. At any rate....back to the original OP. Your set up is FINE. PLENTY. Go shoot those big bulls I was telling you to earlier and you will love the results on broadside shots a lot of the time....and after shooting all those bulls you don't.....come talk to me about where you are hunting because that is a good spot! I want to know where you are hunting! lol

[>>>---WW---->]

OK! Will an elk be any deader from a complete pass through than it will with an arrow dangling by the fletch on the off side. Your setup sounds like it should be an elk killing machine. If it ain't broke, don't fix it! And congratulations on your successful hunt.

[Brendan]

Back again to the .223 bullet (a flavorite coyote getter) an extremely light "arrow" that has A LOT more KE than my 450 grain arrow out of the gate. A lot!

This isn't completely a valid comparison... If you want to talk light and fast vs. heavy and slow for it to be a useful comparison - you need to be comparing KE and momentum from the same weapon. i.e. a 350gr arrow vs. 450gr arrow vs. 500gr arrow all shot from the same bow.

A couple other things, first, you also need to consider arrow efficiency. A heavier arrow is more efficient in that less energy is lost to vibration, friction, noise, etc. You are also ignoring momentum - which is mass * velocity, which is the resistance to slowing down. An object with higher momentum will be impacted less by friction and will retain speed downrange better, and will also be harder to slow down when it impacts the target (penetration). Let's also remember that an arrow kills by hemorrhage (penetration) - not shock (energy) like a rifle bullet.

Lastly - I've seen a lot of practical real world tests that agree penetration and downrange efficiency is better with a heavier arrow.

But, it's all a happy medium. Arrow gets too heavy - and if you miss-range a target, and you could have a much bigger vertical miss because of your arrow trajectory. Personally, I have two arrow setups depending on the bow I'm shooting. They range from 6.2 - 7.0 gpp and put my arrow speeds in the 280 - 290 fps range. (72 lb bows, one a 350 ibo, one a 330 ibo)

Curly - I agree with olympus, swede and everyone else, your setup is fine. Arrow speed is probably in the 260-265fps range. My guess is you hit a rib, or two...

[olympushunt]

Definitely agree with ya Brendan. I was simply trying to explain there are more forces at play than simply grains/lb correlating to penetration. I'm not trying to compare bullets to bheads.
They won't be less dead but a pass through is pretty handy when trying to blood trail an animal. More leakage holes.

[Swede]

I don't know what the debate is here. The same bow will transfer more stored energy to the heavier arrow than to the lighter one.

A heavier arrow is more efficient in that less energy is lost to vibration, friction, noise, etc.

That is correct.

You are also ignoring momentum - which is mass * velocity, which is the resistance to slowing down. An object with higher momentum will be impacted less by friction and will retain speed downrange better, and will also be harder to slow down when it impacts the target (penetration).

I would just add that the heavier arrow will resist slowing down more than the lighter one. It is harder to stop a locomotive than a Corvette. It would take more room to stop the Queen Mary than a 20 foot sport boat at anywhere near the same speed.
If you want to experiment a little, just take your bow out to a good target that will stop your arrows. Shoot at the target from 10 feet away with your regular arrow. Now remove the nock and fill the shaft with lead shot and do the same thing. See which penetrates deeper.

[Brendan]

Definitely agree with ya Brendan. I was simply trying to explain there are more forces at play than simply grains/lb correlating to penetration. I'm not trying to compare bullets to bheads.
They won't be less dead but a pass through is pretty handy when trying to blood trail an animal. More leakage holes.

Agreed - now if we can just put this into practice!

I would just add that the heavier arrow will resist slowing down more than the lighter one. It is harder to stop a locomotive than a Corvette. It would take more room to stop the Queen Mary than a 20 foot sport boat at anywhere near the same speed.
If you want to experiment a little, just take your bow out to a good target that will stop your arrows. Shoot at the target from 10 feet away with your regular arrow. Now remove the nock and fill the shaft with lead shot and do the same thing. See which penetrates deeper.

Agree, we're saying the same thing. The heavier arrow resists slowing down more because it has a higher momentum

At the end of the day, I think these threads just prove we're all stir crazy and can't wait to get back in the woods I don't think I've ever been so excited for spring....

[olympushunt]

Amen.
And now back to our regularly scheduled program.

[WapitiTalk1]

OK! Will an elk be any deader from a complete pass through than it will with an arrow dangling by the fletch on the off side. Your setup sounds like it should be an elk killing machine. If it ain't broke, don't fix it! And congratulations on your successful hunt.

Very good thread folks! The minimum big game arrow weight in many states seems to be about 300 GNs which may be a tad too light IMO. The key, absolutely, is correct arrow placement! As WW mentioned, "Will an elk be any deader from a complete pass through than it will with an arrow dangling by the fletch on the off side." I have shot a good handful of elk where my arrow smashed a rib going in and did not get a pass through but the damage to the inside of those elk was ridiculous as the arrow churned with each lurch of the animal. You may arguably not get the same "quality" blood trail without a a complete pass through (that is subjective also based on the angle the bull runs after hit in relation to the terrain elevation), but the elk will die. That's why we hone our tracking skills over the years, right?

Found this digging around. It's a bare bones archery gear requirements for the states.... Colorado has some odd restrictions "Hydraulic or pneumatic technology cannot be used to derive or store energy to propel arrows. Explosive arrows prohibited.". Man, they're picky down there

http://www.gearheadarchery.com/pages/regulations

[N2mywake]

great thread. yes I'm stir crazy and thinking about KE.. lol

[CurlyTail]

I am also enjoying this educational discussion .

I appreciate the trade off between weight, velocity, and the penetration and trajectory issues. I chose the Magnus Stinger somewhat for the geometry of the head. It is basicly a long skinny broadhead, and it makes sense to my brain than long and skinny will penetrate better that short and fat given the same weight and velocity. I like a narrow tip angle for best possible penetration. I feel that the diameter of the cut is somewhat over rated as I am mostly just trying to "pop the balloon", and a smallish hole does that as well as a huge hole. I was concerned that maybe the 2 small bleeder blades on the 4 blade Stinger might reduce penetration more than it is worth.

Obviously, this entire discussion is moot , if you have good shot placement. It is always the more marginal shots that you hope to optimize your results.

[Swede]

I am mostly just trying to "pop the balloon", and a smallish hole does that as well as a huge hole.

Curly that is a very common misconception. Animals are not killed by "popping the balloon". If popping the balloon is what killed, we could do well with just field points. Massive hemorrhaging is what kills animals shot with a broadhead. The value of a lung shot is that there are a lot of blood vessels in and around the lungs. When shooting down from a tree stand, set 30 feet up a tree, it is common to hit only one lung, still the animal dies quickly and humanely. It is massive hemorrhaging that was caused from slicing through so many blood vessels. And yes broadhead width matters, but again we can lose penetration if the width is too much. It would seem a 1 inch broadhead slicing through 16 inches of critter is at least as good as a 2 inch wide broadhead slicing 8 inches deep.
I fully agree with the other parts of your post. We are best off with a moderate weight of arrow, good balance somewhat to front of center, and very sharp 1 1/18"-1 1/4" tips. Maybe that is what elknut was driving at when he said the best arrow weight to draw weight ration was 6.6 gr/ lb. I did not read the article.

[Lefty]

Arrows are amazing killers.
My daughters arrow on her bull moose this fall was 370gn 26in in Nugent Gold tips with 3-blade muzzy shot at nearly 46 lbs draw wight, the blade was poking the hide on the far side bull the bull went down after 58 yards. My youngest daughter moose was shot two 175 gn, 7mm bullets through the heart, that bull went 160 yards
I based my arrow weight off of the formula I believe Elknut posted a long tie ago,.. maybe on this site?
I like to have a bit more speed on my arrow to reduce drop at further distances,.. I like flatter shooting bullets, and arrows Makes up for my miscalculation on distance.

[Swede]

I based my arrow weight off of the formula I believe Elknut posted a long tie ago,.. maybe on this site?

6.6 gr. per pound of draw weight is not optimal for penetration, but it could give an excellent balance between speed and penetration. I too like a little flatter shooting arrow than some and am willing to forgo maximum KE to obtain better accuracy. I suspect that is really what Paul was trying to present. If he sees this discussion, maybe he will share his findings here again.

[Charina]

An object with higher momentum will be impacted less by friction and will retain speed downrange better, and will also be harder to slow down when it impacts the target (penetration).

Since this is the designated thread for highly contentious hair-splitting physics discussion . . . I thought I'd add a friendly thought to clarify. All things being equal aside from particular mass and velocity combination, a frictional force of X joules of energy will have the exact same effect on both arrows. Both will have the same reduction in energy, albeit, in different relative proportions of their ending velocity due to difference in initial velocity. What is different in frictional forces on the two arrows is the air drag. If you double the speed of an object, the drag quadruples. The faster the arrow, the greater the drag deducts from the arrows energy.

A couple other things, first, you also need to consider arrow efficiency. A heavier arrow is more efficient in that less energy is lost to vibration, friction, noise, etc.

Aside from the greater effects of drag from increased speeds, this is where it is all at IMO. The heavier the arrow, the more energy the bow can impart into the arrow. Not just in overall kinetic energy, but directional momentum as well. A light arrow may zip along at impressive speeds, but simply cannot absorb as much of the bow's energy. This is, in my unprofessional opinion, the primary factor differentiating between effectiveness of light vs heavy arrows. It's not that the friction of air or flesh/bone penetration has an appreciably different effect on the energy available for penetration - it is all about how much energy the arrow starts off with when it leaves the bow. At some point this is a matter of diminishing returns, but for the typical arrow, we can be pretty confident the heavier one comes out with more energy than the lighter one. Intuition (and some reading of Dr Ashby) tells me that the tipping point is above 6.6g/lb. Perhaps that is true for older or low poundage bows, but with a 70lb fast cam bow - I think its well higher than that.

[Swede]

Here is a part of an article I had published a number of years ago after doing some testing with my chronograph. I think you can get the drift of what was happening with the light and heavier arrows. All of the shots were from the same bow with no change or adjustments.

"In this test, I shot two arrows, ten times. Each was shot five times at 0 yards and five times at forty yards. The variation of the arrow speeds in each group of five was never more that one foot per second, from the average. The 350 grain arrow passed through the chronograph at 260 feet per second (52.5 foot pounds per square inch) at 0 yards and 242 feet per second (45.5 foot pounds per square inch) at forty. The drop in kinetic energy was 13.3 percent. The 500 grain arrow was traveling at 224 feet per second (55.7 foot pounds per square inch) at 0 yards and 212 feet per second (49.9 foot pounds per square inch) at forty yards. The drop in kinetic energy over 40 yards for the heavier arrow was 10.4 percent."

[Charina]

Thanks for putting those real world numbers out there Swede. And I concur with your calculations of ft-lbs of energy - sorry, the CPA/auditor in me compels to me verify.

I'll add that the 500 grn arrow had 6% greater energy coming out of the bow than the 350 (bow efficiency of energy transfer to a heavier object). And it had 9.6% greater energy at 40 yards - (combination of energy transfer efficiency, and drag differential from higher speed of lighter arrow).

CurlyTail - if I were you, I wouldn't change a thing if its all tuned and stable. No need to fix something that aint broken. Lack of passthrough isn't a sign it's broke, as I have read of many heavy well tipped arrows not achieving full passthrough. It's all in where it hits. You got the elk, right? Double lung, right? Decent blood trail, right? Sounds like success to me!

[Swede]

Obviously the bows did not shoot as fast back in those days, but the math was the same. Anyway it is good to have someone check my math. I am definitely not infallible.

[ishy]

Curly we shoot pretty similar setups, and I shoot both 2 and 4 blade stingers. After lots of years and lots of animals taken with our group we usually stick to 2 blade stingers for elk. We'll use the 4 blades for bear and deer, but like that extra penetration for elk.

[Beendare]

Arrow energy is going to continue to increase as the weight of the arrow goes up that's a fact. Not only do to the increased momentum of the heavier arrow but also due to the fact that the heavier arrow absorbs more of the Bows energy.


That loud noise you hear when you shoot a light arrow from a compound bow versus the quieter sound from a heavier arrow is excess energy in the bow that wasnt transferred to the light arrow. The excess energy exhibits itself as vibration and sound

In fact the whole penetration thing is very easily explained. You don't need a formula to figure it out. If you want to increase penetration all else equal just add arrow weight it's that simple.

Curly, your setup is sufficient ....so my guess as to why you arent getting the penetration you should is Poor arrow flight. And thats because your arrow isnt assembled perfectly or your bow is in Broadhead tuned. My guess with those skinny shafts is those outserts have a lot to do with your problem. Those outserts are notorious for imperfect straightness.

Easy to check, put them on an arrow spinner to test. You can try spinning them on a table and looking for a wobble but in my experience it's hard to see a wobble that's less than .004 inch. If you have any wobble at all those arrows are not flying perfectly even though it may appear to with the naked eye.

Poor aero flight kills penetration . Even an imperceptible wobble will screw you up. Think of your aero as a straight line of ball bearings. If that arrow hits at a slight angle a lot of the energy is lost. If that line of ball bearings hits in a perfectly straight line every ounce of that assists penetration .

[CurlyTail]

Curly we shoot pretty similar setups, and I shoot both 2 and 4 blade stingers. After lots of years and lots of animals taken with our group we usually stick to 2 blade stingers for elk. We'll use the 4 blades for bear and deer, but like that extra penetration for elk.

Now that is a helpful reply, based on real life experience - invaluable!

[CurlyTail]

Poor aero flight kills penetration . Even an imperceptible wobble will screw you up.

I had not considered this, and this point seems to have merit. Is it possible to have poor aero flight, but still be hitting your aiming point? I do sometimes think my arrow is not stuck in the target perfectly perpendicular, but the point of impact is pretty good.

I did spin my arrows again prior to the season, and ended up discarding several with slight wobble. I only hunted with my best arrows. I am a beginning arrow maker, so some slight imperfections in assembling the arrow are a realistic possibility.

[Heartwood]

Curly's arrow will kill all kinds of elk at its present weight,i believe it is just not at its optimum weight. My take on Elknuts testing on arrow penetration is this: 1. 1. He took math out of it and just looked at physical outcomes. 2. He shot arrows into a uniform substrate. No, it was not actual tissue but more simulated a hit into bone instead of hide and muscle. After all most shots into just hide and muscle would result in a passthrough. 3. He found that increasing arrow weight did result in increased penetration but only to a point, then penetration started to drop off. I'm not going to try to explain these results with math, but i believe his findings are beneficial to fine tuning our selection of arrow weight for hunting.
If in doubt, read about his testing and results. I think there were many pages of discussion on archery talk forum.

[Beendare]

Poor aero flight kills penetration . Even an imperceptible wobble will screw you up.

I had not considered this, and this point seems to have merit. Is it possible to have poor aero flight, but still be hitting your aiming point? I do sometimes think my arrow is not stuck in the target perfectly perpendicular, but the point of impact is pretty good.

I did spin my arrows again prior to the season, and ended up discarding several with slight wobble. I only hunted with my best arrows. I am a beginning arrow maker, so some slight imperfections in assembling the arrow are a realistic possibility.

^thoughtful/ honest response....how refreshing!

Yeah, if you haven't BH tuned...its arrow flight...and
if you haven't spun your arrow on a jig.....they probably aren't assembled perfectly. I did a test years ago [when I used to be able to shoot!] I used a micrometer and took a group of BH tipped arrows identical in size,weight and spine from a tuned bow with the only variation being the BH's straightness. 3 groups; .006",.004" and .002" striaghtness.

I could hold the sub MOA groups I shot with my FP's with the .002" arrows [3" or under at 40 yds] but the .004" were about double that and the .006" had notice-able corkscrewing in the first 15 yds of arrow flight with even worse groups. It makes sense....thet first 2" is critical with a BH. If its not perfectly straight you are going to get a little bit of steering off course.

I'm putting together something that should help you on arrow assembly......give me a couple days.