I’m an admitted bowhunting tinkerer. I’m always looking to learn more. I will start by saying this not a speed thing. Speed is easy to figure. Less weight equals more speed but I’m thinking in terms of a bowhunting setup rather than a 3D, target setup. By more I mean efficiency from the bow and increased penetration. I talking in terms of the Kinetic Energy (KE) and Momentum (MO) outputs compared to draw weight and arrow weight so I started messing around with my arrow weight. For this test I used an older Bowtech (2006 Justice) set at 64 pounds. I used a variety of tip weights and arrow tubes and weight washers to hit the grain weights exactly. I used a “Chrony” brand Chronograph. I started with an IBO arrow weight of 5 grains of total arrow weight (all components) per pound of bow draw weight. This is the arrow weight that advertised speeds are derived from. I then experimented with increasing arrow weights. The following results were achieved. Arrow wgt: 5 grains per pound of draw x 64 Lbs = 320 grain arrow. Arrow speed (5 shot average): 277.5 FPS KE: 54.5 ft/lbs MO: .393 Efficiency factor (KE divided by draw wgt): 54.5 divided by 64 = .843 Next I tried 6 grains per pound Arrow wgt. 6 grains per pound of draw x 64 = 384 grain arrow. Arrow speed: 256.1 FPS KE: 55.9 ft/lbs MO: .436 Efficiency factor (KE divided by draw wgt.): 55.9 divided by 64 = .874 Next I tried 7 grains per pound of draw Arrow wgt. 7 grains per pound of draw x 64 lbs = 420 grain arrow. Arrow speed: 238.3 FPS KE: 56.4 ft/lbs MO: .473 Efficiency factor (KE divided by draw wgt.): 56.4 divided by 64 = .883 Next I tried 8 grains per pound of draw Arrow wgt. 8 grains per pound of draw x 64 lbs = 512 grain arrow. Arrow speed: 226 FPS KE: 58 ft/lbs MO: .513 Efficiency factor (KE divided by draw wgt.): 58 divided by 64 = .908 Next I tried 9 grains per pound of draw Arrow wgt. 9 grains per pound of draw x 64 lbs = 576 grain arrow. Arrow speed: 214 FPS KE: 58.5 ft/lbs MO: .547 Efficiency factor (KE divided by draw wgt.): 58.5 divided by 64 = .915 Next I tried 10 grains per pound of draw Arrow wgt. 10 grains per pound of draw x 64 lbs = 640 grain arrow. Arrow speed: 203 FPS KE: 58.5 ft/lbs MO: .576 Efficiency factor (KE divided by draw wgt.): 58.5 divided by 64 = .915 Next I tried 11 grains per pound of draw Arrow wgt. 11 x 64 = 704 grain arrow. Arrow speed: 190 FPS KE: 56.4 ft/lbs MO: .593 Efficiency factor (KE divided by draw wgt.): 56.4 divided by 64 = .881 Seeing I crossed the point of diminishing returns in efficiency and KE, I didn’t go any farther. At the bottom of this you will find a graphical representation of the above data. Allow me to ponder. Back in 1985 I bought a compound bow and used it for 21 years before buying the BowTech mentioned above. That old bow set at 70 pounds and shot a heavy aluminum arrow with a 145 grain broadhead a blazing 197 feet per second. By today’s standards, such a bow could never kill a deer but with that bow I killed countless deer as well as bear and small game and other critters and I always got a pass thru. I cannot recall a single instance where any game animal ran off with my arrow. As far as this test goes, as expected, heavier arrows provided more power and efficiency but only to a point. It would appear that the sweet spot that can obtained from this bow comes from using a 9 grain per pound of draw weight arrow even though momentum continued to increase. Regardless of the bow you use, there is an arrow weight that will provide the maximum impact performance and efficiency. That being said, arrow lethality is not any one single factor but is a combination of several factors. 1. Shot placement (no amount of math will make up for a poorly placed shot) 2. Broadhead sharpness and design. 3. Impact force (KE and MO) Provided you can hit your target, having all 3 will maximize arrow lethality with shot placement trumping all but in the real world of bowhunting, things happen that are beyond our control. There will be times when shot placement is not what we would have hoped for and that’s we rely on broadhead sharpness/design and impact force to bail us out of a less than perfect situation. Since we as bowhunters have control over the efficiency of our bow arrow combination and broadhead selection, we would do well to maximize those aspects of our set-up. Are you getting the most out of your bow/arrow combination? Would a heavier arrow/broadhead combination give you that edge when things don’t go exactly as planned? You no doubt paid top dollar for your hunting rig so why not get the most from your investment by squeezing every ounce of killing power out of your investment? You bought your broadheads based on a combination of hunter recommendation, hunting shows and magazine ads. You bought your arrows probably based on name and what the spine charts told you to use but neither of these are customized to you and your bow to perform at optimum bowhunting conditions. The modern compound bow market is stuck in the speed fad and all advertising seems to be based on feet per second as if that were the end all and be all of bow performance. Speed is only one part of the equation. But the current fad is speed and from a bowhunters perspective we consider speed when thinking in terms of things like yardage estimation but rangefinders have all but negated that. Another consideration for arrow speed is the effect of speed in regards to a deer’s ability to jump the string but please consider the following. If your bow provides the maximum in performance with a heaver arrow at 250 FPS vs 300 FPS you are still better off with a more efficient performing bow/arrow because a few FPS means nothing to a deer’s ears since sound travels from your bow to a deer at 1,126 feet per second. A few feet per second of bow speed pales in comparison to the speed of sound. Even with the fastest bows on the market at 360 FPS, the sound of your intentions will reach the deer more than 3 times faster than your arrow will. Having bowhunted for 35 years and knowing many many bowhunters I can say with great confidence that bowhunters are some of the cheapest hunters on the planet. We are always trying to do the most by spending the least but is saving a few bucks robbing you of a few big bucks or does or antelope or bear? Arrows are not cheap but weight tubes and broadhead weight collars are so you have the ability to maximize (or at least improve) your bow’s performance without breaking the bank. We tend to spend a boat load of money on a bow but scrimp on the things that kill game (arrows and broadheads) Perhaps after spending all that money on the broadhead delivery system, there is little left for the one piece of gear that actually kills the deer. After experimenting with the performance of your bow you have to ask yourself some questions. Is the 100 grain broadhead market where you should be shopping? Will your rig perform better with a 125 or even 220 grain head? Are 7.8 grain per inch arrows better penetration or would 9 grains per inch perform better? The off season is long but it gives bowhunters the opportunity to refine and experiment to put the odds in their favor. So how does the hunting archer test and evaluate and experiment to get increased performance for his bow? You will need a chronograph. If you don’t own one, perhaps your local archery club does (another good reason to be affiliated with a local club). You can also visit a local archery dealership and for a few dollars and with an assortment of field tip weights, weight washers, weight tubes, weed trimmer line and even masking tape to get you to the weight you want, you can find out the sweet spot that will give you better performance from your bowhunting gear. Perhaps you can maximize performance with a few weight collars and/or a weight tube inside your arrow. Using weed trimmer line to boost your arrow weight which reminds me of a story. I was contacted by a whitetail bowhunting friend who planned to go out west on an American bison hunt and he was looking to optimize the output from his 70 pound compound. He knew his 375 grain whitetail arrow was not going to cut it for such a big animal. After a little experimenting we ended up with brass inserts, a 200 grain broadhead and 4 lengths of weed trimmer line inside his arrow which brought him to a hefty 700 grain arrow (10 grains per pound of draw). The performance and penetrating ability of his arrow ended the life of a 1,700 Bison at 35 yards. His arrow passed through both sides of the chest of the roughly 3 foot wide beast. This might be a bit extreme for thin skinned whitetails but hopefully you get my point. Maximizing a bows output puts the odds in your favor for making a quick, clean, good penetrating and ethical kill regardless of the size of your prey. If speed is your thing, the answer is easy, shoot an IBO weight arrow weight but I caution using an arrow lighter than that since less than 5 grains per pound of draw risks voiding your bow’s warranty so be aware that too light an arrow comes with some risks. There were other things I noticed as I increased arrow weight. Bow noise and vibration felt in the hand dropped as arrow weight increased. Both are a good thing for bowhunters. Also, there was a noticeable increase in penetration into my target as I reached 11 grains per pound of draw due to the ever increasing momentum. This pondering turned out much lengthier than I originally anticipated, thanks for listening. I hope you were able to pull something of value from it.
How much of a difference is 4 ft/lbs going to make? With a 640 grain arrow which is double of your 5 grain minimum, you gain 4 ft/lbs and lose 73 fps. Help me understand the reasoning. Is 4 ft/lbs a BIG difference? Thanks for taking the time to post.
Very interesting and extremely detailed... but how far does it need to stick into the ground on the other side? :D :p -Coming from someone who rocks a 330grn arrow. Very cool experiment seeing just where you top out at on KE before you start to lose performance. That's some serious "tinkering".:D
4 foot pounds and the increase in momentum and efficiency will be seen in penetration should the unthinkable happen and a boney mass be hit or the game animal presents a shot angle increasing is cross sectional area (quartering away). The loss of fps means little since speed alone never killed a deer and is only a recent marketing fad. A well placed, sharp broadhead with ample impact force and momentum will kill a deer even if its 74 FPS slower than some IBO number. While arrow speed dropped by 74 FPS, KE, MO and efficiency all went up. This equals increased arrow lethality. As I stated, if speed is the most important thing to a bowhunter, then they can disregard these results as any loss in the speed number will be met with much objection even if it costs them efficiency and penetration and lethality and well as available choices in broadhead and arrow selection as well as shot angle selection choices.
Oh Rancid... I think we might just somehow be related either that or we're both a tad over analytical. 'Twix last season and April, I experimented with different overall arrow weights for my setup. I ended up with an arrow weighing 8.4 gr/lb before my bow's efficency rating started going south. GREAT POST!
All valid, however I too am curious what 4 ft/lbs gets you. I couldn't care less about how fast my bow is, all of the more modern bows will kill deer. But I am curious of what 4 ft/lbs means down range. Does it mean a half inch more penetration, two inches? That's what I'm curious about. Thanks and great thread overall.
IMO 4 ft/lbs gets you exponentially more forgiveness on your shot. Forgiveness with respect to error. In others words 4 ft/lbs gives you a much bigger margin for error. If a person does not feel the need to increase their margin for error then 4 ft/lbs won't mean much. It will also give your arrow more "punch" downrange, 30+ yards, which may matter for some of those whose max range is that far.
One other factor in a heavy arrow is the amount of drop. I think a compromise of speed and weight equal flat shooting which can lead to less mistakes in yardage. The amount of drop has to play a role in the best compromise of weight to speed ratio. If a hunter never shoots out past 20 yrds then this a non issue but if he shoots 30 plus this could be a factor. Just some thoughts on your test.
I've posted about this experience before... but several years back, I was shooting a local 3D tourney with Jeff Propst and his son (some of you may know them from the Drury DVD's). Jeff was preparing to go on an elk hunt, and wasn't shooting to win the tourney as I was; he had his bona fide elk setup with him and was just wanting to get some practice in. It was a fun day sharing stories, but what I came away with was just how much more his arrows were penetrating the targets. I was shooting at close to 5 gr/lb that day, and I was getting a couple inches of penetration into the foam... he was more like 9 gr/lb and his arrows were going in half a foot!! Literally, I sometimes was having to put my knee against the target to pull his arrows; no such problems with mine. THAT'S what 4 extra foot-lbs. will give you.
I'm pretty sure he did. I know I did. My arrows now weigh 530 grains. Out of my 70# Drenalin they're only moving at 258 fps, but they make my bow so quiet and so vibration free that I took my stabilizer off. There's no need for it. As Brucelanthier said in another thread, it's a very forgiving and and unstoppable arrow setup.
Actually, that was only my 3D setup... I'd already been hunting with heavier arrows and higher FOC. I'll admit, I DID use a similar arrow when I went out west in pursuit of antelope, because I'd been told that basically if you hit them anywhere you can recover them because they're fairly fragile in terms of big game, and they have no place to hide -- which is somewhat true. I opted for the speed route on that trip... The next time I hunt antelope though, I'll go after them with my whitetail setup... not that the antelope needs that heavy an arrow, but because I experienced a significant amount of wind drift on my shots out there on the open plains with such a light arrow.
I suppose that makes sense. I actually moved from a 10.2 gpi arrow to a 9.3 gpi. I got tired of having to grab my arrow puller when I was shooting targets. I haven't noticed any real difference in noise, but I rarely have to grab the arrow puller anymore.
I'm afraid if I go with a heavier head then my arrow will be too weak. Any of you guys tried the weedeater string trick for adding weight?
I have not tried the weedeater trick but, if i were to add weight by total, I would give these a try. They are 12 for $12. http://www.3riversarchery.com/Product.asp?show=info&c=57&s=228&p=0&i=6731X#full
Donnie, I had to have someone run my desired setup through one of the archery programs (i.e., TAP or OT2) to ensure the move I was making for my desired weight this past year was correct for that very reason (I'll decline to mention his name for fear of him being inundated with similar requests... Believe it or not, as many bows as I've set up over the past couple decades I'd never purchased that software because all my bows have been so similar in their setups). By going to Muzzy's new steel-ferruled MX-3, I automatically added 25 grains up front (125 grains vs. the older model's 100). I was WANTING to go with a 100-grain brass insert, but discovered there wasn't a shaft made that would spine out right for that setup (Thankfully Muzzy was awesome about switching out my seasonal order of brass inserts for me...). I went back to my old 50-grain insert, but that STILL left me with needing to drop down from a 350 spine (Victory VForces) to a 300. Definitely something to think about. Bruce, that video is really intriguing... obviously, I've heard of folks utilizing such a method in advance of heading to the Dark Continent and other such excursions... would inserting a full-length tube such as that change the dynamic spine at all?
It should not affect the dynamic spine as far as I know. I would use those as a way of adding weight without using a brass insert. They would probably also be useful for those with shorter DL's and shorter arrows to get some extra weight for their setup too. Some day I am going to use them just to use them and see how they work out.
I ordered some Gold Tip XT hunter 5575's last week so I'll just stick with them. My plan is to use the same arrow setups with two different bows, a 2009 Admiral 60/70 and an Assassin 50/60. I'm not sure if this is feasible. Maybe I could make each setup's arrow weigh the same with the exception of the broadhead weight. I don't know...got some figuring to do. I better get on the ball. Decided to mess with the Assassin today and do some fine tuning. Now, it's all jacked up. :D The broad heads will not close the distance no matter how I move my rest. Put new strings on my Admiral last week and discovered the axle to axle measurement was more than an inch off. Come to find out...the string maker made the strings too short. He's making it right though. I just need to get both bows ready before October 1st. Not really concerned but I have to get on with it. :D
Well, I just got home from work and weighed the weedeater string...an inch didn't even register. I do have a bunch of CAT 3 cable lying around that was being thrown out at work. One inch of the CAT 3 was approx 10 grains. I think I found a winner.
