If you take a 375 grain arrow, and a 500 grain arrow, both carrying 70 ft/lbs of kinetic energy at the point of impact, they will both penetrate exactly the same. They have to, they have the same energy, it's simple physics. Now, if you shoot the two arrows mentioned above out of the same bow, the heavier arrow will absorb, and therefore carry, a bit more ke. But the difference is small. Momentum is a factor too, but not that much with the normal differences in arrow weight we use. If we could somehow shoot a 200gr arrow versus a 600 grain arrow, then momentum difference would become more noticeable, and the lighter arrow would slow down faster, but even then not all that much at normal hunting ranges. I used to buy into the "heavy arrow penetrates better" theory, but, under normal hunting circumstances, the facts of physics just do not support the theory.
No, they won't penetrate the same. The lighter arrow will react to the resistance met at a much greater scale than the heavy arrow.
Its hard for me to not have a somewhat biased opinion as I hunt much heavier boned animals out here (elk, bear, even mule deer). Curious as to what you would say your average shot distance is? Nice to have a conversation on the boards for once with a mutual agreement on separate arguments.
Average shots taken are anywhere between 20-35 yards. I've honestly thought about trying some heavier arrows, and probably will one day just to see for myself... I almost bought some FMJ's this year. I'm not Biased one way or another, Just looking at both sides here, and I just happen to be on the light side right now, and it's been working for me.
I copied this from here. If anyone really wants to learn something it would be beneficial to read more of Dr. Ashby's reports. http://www.alaskabowhunting.com/Ashby-On-Momentum-Kinetic-Energy-Arrow-Penetration-W19.aspx It is common for proponents of light and fast arrows to counter that the faster arrow will have traveled a greater distance through the tissues in the same time period than will the heavier, and slower, arrow.This would be valid were it not for the nature of resistance forces. As the arrow’s velocity is increased the resistancedoes not increase equivalently.The resistance increases exponentially.The resistance of a medium to penetration is reliant on the square of the object’s velocity(assuming objects of a given coefficient of drag; i.e., using arrows with the same external profile, material and finish).In other words, if the arrow’s impact velocity doubles, the resistance increases by a factor of four.If the impact velocity quadruples, the resistance to penetration increases 16 times! The effect of exponentially increasing resistance is easy to experience.Try holding a hand out the window of the car, while the car is going at a velocity of 30 miles per hour (which is only 44 feet per second), and feel the air’s resistanceagainst your hand.The resistanceis very slight.Now accelerateto 60 miles per hour (a mere 88 feet per second).The velocity has only gone up by a factor of two, but the air’s resistance to your hand passing through it is now four times greater. Now imagine the effect on an arrow passing through tissues.Tissues are more solid than air.They have a greater density.Their resistance to an object’s passage is higher.Visualize the effect as an arrow’s velocity increases from 150 feet per second (a fairly typical velocity from a mid-draw weight traditional bow) to 300 feet per second (as from a top line compound bow). Let us now assume an arrow weighing 700 grains for the slower bow (150 fps is easily achievable with that weight arrow and a ‘traditional’ bow) and a 390 grain arrow for the faster bow (the advertised velocityrating for one of the newest compound bows on the market, using that weight arrow).The slower arrow has 0.466 slug feet per second of disposable net force.The faster arrow has 0.519 slug feet per second. Lets also assume these two arrows are of same materials, have equal physical external dimensions (easily achievable), and both have perfect flight characteristics.The tissue’s resistanceincrease is totally dependant upon the velocity of the arrow. The lighter arrow has 10.22 percent more disposable net force (and 123.2 percent more kinetic energy) than the heavier arrow but, because of its higher velocity, it is met by four times the resistance to penetration.Which arrow will penetrate further in real tissues?Empirical evidence from the outcome studiesprovides an overwhelmingly definitiveanswer.Both the frequency and degree to which the heavier, slower, arrow out-penetrates the lighter one is of such a magnitude that it must be viewed as the norm. ALL MOMENTUM IS NOT THE SAME Given two arrows, identical in shaft and broadhead materials and profile, and having EQUAL momentum, but possessing UNEQUALmass, the arrow deriving the greater portion of its momentum from its mass will penetrate better.The Laws of Physics requires this to be true, and ALL of my field test data validates this to be the case. To say this in another way, arrow momentum derived through increasing arrow mass results in a greater gain in penetration than doesmomentum gained by increasing an arrow’s velocity.This is true because the tissue’s resistanceis increased by the square of the velocity.
Understandable. What is your arrow length, draw weight, etc.. I may have some arrows made up you could try if interested?
Ill elaborate on my "longer effective range" statement. I should have added "when taking sound into consideration when shooting a game animal". I do agree a slower heavier arrow is the way to go. However in answering the question "what is the advantage of greater speed and flatter trajectory?" some people may say that the range you can shoot without having the deer "jump the string" is longer with a faster arrow. Speed of sound is about 1100 fps give or take. If you're shooting a given distance at a game animal, the delay between the sound reaching said animal and arrow reaching said animal is shorter when using a faster arrow rather than a slower one. Therefore you could shoot at a deer that is further away with a faster arrow and expect the same speed/type of reaction as animal shot at with a slower arrow at a closer range. All that being said, if you do the math you're looking a fractions of a second difference at reasonable distances (under 60 yds) and its generally accepted that the benefits of a heavier arrow are better than the faster one. Use the heavier arrow and just don't expect to shoot animals out to extreme ranges.
The bow is still going to make some noise. A heavier arrow isnt going to absorb all noise and make a shot completely silent.
No, but it does make an incredible amount of difference. So much, that I would wager that a deer at any given distance will not jump my bow any more than any of todays speed bows. Unfortunately that is an uncontrollable situation that could never be effectively monitored.
Think so? Maybe on the offside... It broke one of my blades. I should of looked more closely. I thought for sure I caught the "Arm" bone.
This is good stuff. Im starting to realize I should increase my setup past 6 grains per pound. Gonna work on that next year. It seems like a little more arrow drop may be a small price to pay for better penetration, forgiveness, and accuracy. You guys are slowly converting me. I'm still curious to see some real data comparing the penetration of the new smaller diameter shafts to larger ones. I get that there will be less surface area for friction, but it seems like most of your drag will come from the broadhead and this is creating a hole that is significantly larger than the shaft. The difference may be negligible. Now if we are talking about foam targets, then you should see better penetration with the smaller shaft.
^^ I would also like to see solid evidence supporting better penetration on small diameter shafts. Specifically 17/64" to 5/16". Sent from my ADR6350 using Tapatalk 2
IMO, there is more much more drag during penetration when using plastic vanes such as blazers, taller and stiffer, and that vane drag makes much difference during penetration than shaft diameter. If I were worried about drag during penetration the first thing I would do is change from plastic vanes to feathers. Feathers collapse when they encounter resistance which really reduces any drag friction and reduces the drag produced by the vane encountering hard surfaces (bone).
I have heard that smaller diameter shafts penetrate a tiny bit better based on the decrease in friction. Also, if your broadhead does not seat seamlessly or at least a little bigger than the diameter of your arrow, the result is increased friction and decreased penetration. That being said, I shoot thicker aluminums! lol
Agreed. This ^^ a thousand times over. Also, a lot of people posting here are seeing the friction / surface area relationship incorrectly. Friction does not increase or decrease with an increase or decrease in surface area. Friction is increased or decreased by the pressure applied to two opposing surfaces. If the pressure between two surfaces is constant and the surface area decreased, the same amount of pressure is still applied albeit to a smaller surface area. Same amount of pressure = same amount of friction (assuming both surfaces act the same under higher and lower pressure loads). The "key" to smaller diameter shafts increasing penetration relies on a standard broadhead ferrule making a hole larger than the diameter of the arrow. This allows the arrow to pass through a hole with much lower pressure between the surface of the shaft and the tissue/bone of the animal. Lower pressure = less friction. Less friction = less energy lost to friction and more energy available to continue momentum through the animal. Again, all this is most likely negligible in real-world applications (killing deer). No two shots are the same, there are fluids that lubricate the arrow as it passes through, etc. The math is correct so manufacturers can say "Better penetration". What they should say is "Better penetration but realistically, it's not a mind-blowing difference when shooting live animals".
I'm not sold on the smaller diameter arrow gets better penetration. It's hard to argue with Ashby though, the guy has done some great testing. For 13 years I shot (fence post's) 2216's out of my recurve. I'd say at least 90 to 95% were complete pass throughs. These arrows were 560 grains shooting a 1 1/4 3 blade Snuffer. I have no complaints In the least with this arrow. The last 4 years I've shot 340 FMJ's. A MUCH smaller arrow In diameter. I can't comment on the penetration factor vs my aluminum's yet as I've only shot 3 animals with them so far. So far the only thing I've found out that's In my favor with the FMJ's Is that you can get a much higher FOC then I could with my aluminum's. FMJ's flex much easier then that of my 2216's and there forgiveness In tuning Is much higher.
