I have always guessed at the speed of my bow and figured my kinetic energy from my estimation on speed. I am shooting a 550 grain arrow and my bow is 55# @28 and I draw to 29". According to my easton bow scale I am right at 57#. Well I took the guessing out of my speed estimation and shot my setup through a chronograph 165 fps ( I was guessing more like 190) . This calculates out to 33.3 ft lbs. of kinetic energy. I honestly always figured I was closer to 45- 50 ft lbs. I am sure my set up is more tnan ample for sny of my hunting situations , just thought I was packing a little more punch.
That 165 fps doesn't seem right at 29" and a bit over 9 grains per pound. Just my experience.
165 fps would pretty much be the speed for a selfbow with those specs.
Blacky
Buffalo bow shot at 10 gpi @ 28", braced at 8" with the stock string and string leech silencers under shooting machine is around 175-177 fps at 1 yard in front of the bow, if you add 1 inch of draw (thus 3# to the bow) with same bow and arrow you increase that speed about 6 fps, so 181-183fps. With a clean release you will loose something around 5 fps (little more or little less) so you could expect really something more in the 175-180 fps range.
Maybe real draw lenght when you let the string isn't 29" ?
Maybe release isn't so clean?
Maybe chronograph doesn't give the true speed (sometimes light related issues) ?
Maybe arrow is heavier than you think?
Seems like you should be getting a little more speed, but your set-up is plenty for anything crawling around our continent.
try another crono
KE is a very poor measure of an arrows ability to penetrate. Impulse momentum is the measure you are looking for. KE is a measure of energy stored in the arrow during flight. It tells you nothing about how the stored energy is released in living flesh. Dr. Ashby covers the IM equation in his reports. You have plenty of punch with your set up to kill NA game.
I shoot a mild R/D longbow - 55 lbs @ 29 inches. 564 grain arrow @ 165 fps. I hunt elk and bear and have worries about penetration.
Exactly. KE is not the way to measure penetrating power. It's a tool for evaluating efficiency between bows.
First off...Good on you for doing some thinking! :thumbsup:
How warm were the temps when you chrono'd it?
I just did a post about losing speed in the cold.
My setup was doing way faster in the summer.
Just tested it again last week and it was 20fps slower. WTH? right.
After checking for tuning and everything since all that would be off if the speed was that much slower.
I found out the chronos will read slow when they're cold.
My setup was still shooting what it did in the summer.
I wouldn't be a bit surprised if you checked that bow at a warm range you'd be up in the 180's at least.
Your setup is fine with more than enough energy.
Most of this stuff was said by others for good reason.
Ashby does go in to the energy pretty in depth.
The easiest way to compare one setup's energy to another's is to simply take the total wt of the arrow and multiply it by the speed.
Doing this will also let you find out with what wt arrow your bow will impart the maximum amount of energy to.
Most of the time, bows throw the highest energy arrow at around 12-13 grains/#.
Might be too slow for you, but there is a trade off with everything.
Kinda fun stuff.
Good luck and have fun.
:thumbsup:
I use Stu's calculator and am often suprised by the KE I see in the far right box. Quite low...For kicks I shot my Talltines longbow through a chrono at a bowshoot. 52#at 28, 620 gr total arrow weight. 165 ft/sec. Start doing the calcs and KE is pretty low.
Then I go to WY and shoot through an elk at 25 yds, Manitioba and shoot through a bear that weighed around 400#, and a giant whitetail here. The bottom line is this: KE is a poor indication of momemtum and how well that stickbow performs. A sharp head, through the ribs with the set-up you described above will kill anything in North America.
boom!
X3 on that speed doesn't seem right. I just shot my 50lb Dorado through my Chrono . I Draw 30 so was getting around 55lb at my draw and I'm using a 550 grn arrow as well and was getting 182fps.
KE is defined as
The kinetic energy of an object is the energy which it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest.
Momentum is the key, like everyone else has said.
Formulas are only part of the equation. An arrow that is flying straight (vs. one that impacts at an angle), sharp broadhead, broadhead design, shot placement, etc. all play a significant part in penetration.
Everything can be perfect on paper and let you down in real life. Know your equipment.
Chad
QuoteOriginally posted by Elk whisperer:
try another crono
Exactly. Check my longbow specs in my signature below with 26.75" of draw length and about the same weight arrow as you. I used my own chrono and it matches other high end chronos I have used before. I have used some cheap(Shooting Chrony brand) chronos before that weren't worth their weight in scrap metal.
Or try another arrow of a different color....a few years back at a shoot with a crono that we found that a crown diped or brighter fletched arrow will give much different results........its all on how the machine reads the reflected light off the arrow.......we had one arrow that shot 200+ out of any bow from 45# to 65# and had a lot of fun with some of the compound guys........
This won't answer any questions, but it may give you confidence in your setup!
From a thread in Hightlights Forum that I read today:
"I was using my 45lb 1966 Bear Kodiak, shooting Easton 2016's tipped with some single beveled 190 grain Tusker broad heads.
The shot took out both lungs, severed the heart clean from the arteries and cut the front leg bone in half just below the shoulder on the opposite side."
Ok I did some more testing today and 170fps is the absolute fastest I can get with my hunting arrows. I tried some 2016 shafts that weigh in at 430 grains and they would shoot about 10 fps faster. But the real kicker is that I shot a round out of my 50# dorado and I get the exact same speeds with this bow as I do with my 55# buffalo shooting the same arrows.
Chronos are funny things. I just chrono tested my tomahawk the other day at an archery shop and with the same arrow I got readings from 121 fps - 171 fps. I am shooting an aggressive d/r longbow 54 @ 27.5" with a 620 grain arrow. I would guess my true speed is around 165 to 170 as I have bows that shoot around 150 and my Tomahawk is much faster.
We always used a 5 shot average when testing out the bows speed. I suggest you try another chrono if possible because no two are alike and you will get different readings from the chrono's.
Lots of folks get really involved in speed. I have seen two bows at the same weight from the same Bowyer shoot different speeds. Now throw in different bow makers and differing draw lengths for shooters and you can' t get any kind of standard. I think the real key is for each shooter to find a set up that works and then optimize their arrows for what they like. A perfect flying arrow with a razor sharp head will kill anything alive today. Placement is the real key to successful kills.
I had a 55# @ 28" Bear recurve [Kodiak Hunter] that I shot thru a chrony years ago. I shot shot 4 shots with 2216 shafts 30 1/2 long 125 gr up front. I draw just over 29". 4 shots were 170-173 fps. I did it again and it was the same. I would feel confident shooting that set up at anything I would ever hunt anywhere,any place! I think the arrows were around 575 GR.
I would`nt sweat it. My set-up a 47@27 Mohawk with a 570 grain arrow shoots maybe 160. I shoot the broadhead through most every critter I shoot and I usually shoot Big broadheads.
When I shot the bow through the chrono the fellas at the "pro" shop were snickering a little in fun till we started talking about how "many" dead critters. The icing on the cake was when I showed them a judo point and told them I set my sights while I hunted.RC
When I was shooting long range highpower rifle I learned why velocity is less important than mass (bullet weight).
Mass is the only part of the equation that doesn't change. All things being equal a light projectile will loose velocity faster than a heavy projectile. When you talk bullets a slow 190 grain .308 bullet at say 2650 fps will outperform a fast 155 grain bullet at say 3050 fps at 1000 yards. Because its not the muzzle velocity that matters but the retained velocity.
The bullet isn't affected by the wind at the muzzle nearly as much as when its 1,000 yards downrange. And a 190 grain bullet will be going faster than the 155 at 1,000 even though it started off slower. Not only does it beat the lighter bullet for velocity but its also heavier and therefore harder for the wind to blow than the lighter bullet. I've shot too many 1,000 yard matches and have proved this to my satisfaction many times over. The guys who worshipped at the alter of speed and shot light bullets consistently got their clocks cleaned by guys who shot big slow bullets at long range. Before someone chimes in and tells me the Palma load is 155 grains I'll let you know that that's a product of the Palma rules and the bullet cannot weigh more than 10 grams. Trust me, they'd be shooting 175-190 grain bullets if the rules allowed.
So how's all this apply to arrows. Well, think about it. First, the observation that kinetic energy is a poor predictor of arrow performance is spot on. There are a ton of factors that diminish the kinetic energy of an arrow. Heat for example...as the arrow goes through flesh the friction from the blade and shaft passing through the animal generates heat. Not much I know.... But that heat is energy from the arrow and detracts from the ability of the arrow to do meaningful work. There are a ton of other factors as well. But the point is that velocity is less important with most trad arrow performance than arrow mass. Obviously this isn't a linear equation. At some point in the curve velocity becomes important. But the mass doesn't change.
550 gr arrows 165-170 fps, sounds bout right to me.
Questions: is it quiet?, Is it smooth? Is it balanced and not too heavy or too light? Does it hit where you look and are you pleased with its feel in the draw and after release? If your answers are yes, you've got a winner in my book.
Macksdad
I was surprised at how slow my Buff was also
Really nice shooting bow but not a speed demon
It even likes a longer hence softer arrow than my other like set ups
From what I have been told by Bowyers like Fedora is that colder makes for faster
I am getting around 175 with a 530 grain arrow out of a 55 pound at 28 inch Buff
It still scales around 54 pounds for me
Maybe your chrono is off try another
Sorry double post
I don't think it really matters unless you are into physics.
QuoteOriginally posted by Kentucky Jeff:
So how's all this apply to arrows. Well, think about it. First, the observation that kinetic energy is a poor predictor of arrow performance is spot on. There are a ton of factors that diminish the kinetic energy of an arrow. Heat for example...as the arrow goes through flesh the friction from the blade and shaft passing through the animal generates heat. Not much I know.... But that heat is energy from the arrow and detracts from the ability of the arrow to do meaningful work. There are a ton of other factors as well. But the point is that velocity is less important with most trad arrow performance than arrow mass. Obviously this isn't a linear equation. At some point in the curve velocity becomes important. But the mass doesn't change.
Ok, work with with me a little here!!
Mass and speed are the two main components of kinetic energy.
Let's say you came home and your wife had cut all of your bows in half, so you decided to end your life by stepping out in front of on coming traffic. I don't know about you, but for me, I would want to pick the biggest and fastest semi-truck I could find, lots of kinetic energy here, I'm talking massive. Forget about the small economy cars.
So what has this to do with arrows? Big and fast = more killing power. I didn't say light and fast!
So does it really matter, I think it does. If we compare apples with apples, such as; Same draw weight, different limb materials, same arrow weight, and then measure the speed of that arrow, and calculate the kinetic energy, we are then able to make a more informed decision about the bows we want to purchase.
For example, if you where comparing two bows of different draw weights, and the lighter bow could produce the same kinetic energy as the heavier bow shooting the same arrow, which bow would you choose? Or, if you knew a particular material would produce more kinetic energy, wouldn't that narrow your search?
Iron sharping iron!
Macksdad,
there's something wrong with your measuring equipment, since an arrow weight reduction of 120 grains only gave you 10 fps more speed.
This reduction should have given you close to 30 fps more speed. FWIW
Blacky
My chrono is brand new, however in todays world that doesn't mean much I am sure it could definitly be faulty. How do I check it, only way I know would be to shoot something with a known speed through it. Like a rifle that I know the muzzle velocity of or put it side by side with another chrono.
QuoteOriginally posted by Blacky:
Macksdad,
there's something wrong with your measuring equipment, since an arrow weight reduction of 120 grains only gave you 10 fps more speed.
This reduction should have given you close to 30 fps more speed. FWIW
Blacky
No Blacky, thats sounds correct.
10 gr add weight is close to 1 fps loss of speed for trad gear. The speed loss you mention is what happen more likely with compound bows (10 fps for 30 gr)
I've chronographed a lot of bows. Most good bows will shoot a 9 gpp arrow at 180 fps with finger release and 28" draw.
Your Buffalo is shooting a 7.6 gpp arrow at 180 fps with a 29" draw?
The bow is slow, or the chronograph is way off. Probably the latter.
- Dave
I learned this the hard way. If you are happy with your bow don't shoot it thru a chrono. ;)
I beg to differ hybridbow hunter. I test trad bows since 1996 with a shooting machine and have done extensive testing with different arrows. It takes 3 - 6 grains of weight to gain or lose 1 fps in speed. At least thats my finding with over 100 different longbows and recurve bows tested. :)
Blacky
How far would you stand from the crony when testing?
I look at it as stated earlier. If your happy with you bow stay away from the chrony. I seen several bows damaged just so the shooter could say my bow is the fastest.
Troy
My chrono just said my Centaur Carbon Elite shot a 420 grain arrow at 50@27" my draw, at 171 fps. Im pretty sure its off.
MCS, I was standing at various distances from 5 ft to 20 ft. ,and I am very happy with the performance of my bow. I was just curious as to the real numbers of its performance. I dont plan on changing my setup at all. Just was surprised at the numbers.
Blacky,
with respect 2 to 3 fps variation for 10 gr is too much.
i and few other friends on the french traditional archery hunting forum also tested most of bows of north american brands and bowyers products. We do our testing under strict protocol using shooting machine, accurate bow weighting for draw force curve. Bows are tested all with astroflight 12 strand pre stretched string custom made for each bows and bows are tested ready-to-hunt with average brace height (according to the bowyer) and same string silencers put at 1/4 of string length . Our test are devoted to give the performance that "Average Joe" will get from the bow in real life conditions for hunting from 8 gpi to 14 gpp. Our tested bows are the bows we purchase as customers,( most of all are in the 48-53# @ 28" range), so there is no commercial bias nor "specially-made-for-test bows".
If you look to the following graphs of several different , but fairly known, bows and brand you will see that whatever the bow design or level of performance for a given design, 10 gr leads to approximately 1 to 1,5 fps variation for 100+ gr weight modification
As exemple here you can see very fast hybrid (ACS), fairly fast hybrid (Fedora xtrem), fairly fast recurve (RER) and low average speed recurve (BW PSA)
All graphs are done by one of us, engineer and physics university professor. Him and i, as a neurosurgeon, are really concerned about accuracy and rigorous scientific approach when doing this (as hobby LOL)
Regards
Laurent
For each bow (BLUE LINE= speed) 1st Graphs is arrow speed/arrow weight in grain and 2nd Graph is arrow speed/ arrow speed in gpp
(GREEN LINE is "rendement"=dynamic efficiency )
(RED LINE is "energie cinetique"=kinetic energy)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/ACS-3.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/acsgpi.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/fedora-1.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/fedoragpi.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/PSA.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/psagpi.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/RER-1.jpg)
(http://i758.photobucket.com/albums/xx225/hybridbowhunter/rergpi.jpg)
hybridbow hunter, impressive stats. Difficult to follow, but impressive. :saywhat:
Blacky(R. Blacky Schwarz) is the dude who does all the bow testing for Traditional Bowhunter magazine. I'm pretty confident in his results/experience.
Maybe your testing parameters are somewhat different, resulting in different results. :dunno:
In my opinion, the difference isn't worth argument.
Laurent,
I just checked your graphs and must say: nice work. As you may know I'm doing a lot of reviews for various magazines and my testing guidlines are also very strict.
Looking at your graphs I could see the following:
ACS: total weight difference is 300 grains, speed loss/gain is 45 fps = appr. 6,7 grains for 1 fps.
Fedora: total weight difference is 300 grains, speed loss/gain is 41 fps = appr. 7,3 grains for 1 fps.
Black Widow: total weight difference is 300 grains, speed loss/gain is 49 fps = appr. 6,1 grains for 1 fps.
RER: total weight difference is 300 grains, speed loss/gain is 42 fps = appr. 7,2 grains for 1 fps.
I'm testing my bows with 6 to 10 gpp, so my findings are different, especially with foam core limbs. I used part of your charts and looked at the lighter arrow weights. If I take the part between 550 grains and 400 grains I see the following:
ACS: total weight difference is 150 grains, speed loss/gain is 26 fps = appr. 5,7 grains for 1 fps.
Fedora: total weight difference is 150 grains, speed loss/gain is 22 fps = appr. 6,8 grains for 1 fps.
BW: total weight difference is 150 grains, speed loss/gain is 25 fps = appr. 6 grains for 1 fps.
RER: total weight difference is 150 grains, speed loss/gain is 22 fps = appr. 6,8 grains for 1 fps.
If you go towards 6 gpp you'll get close to 3 - 5 grains for a speed difference of 1 fps, especially with ILF limbs. This thread shouldn't end as a pi$$ing contest, but you can see that my numbers even match your charts. I never tested bows over 11 gpp, so you have the edge in this department. When I do quick calculations, I use 4 to 5 grains for 1 fps, which ever is easier to calculate.
Blacky
Sure they are !
ours test bows are done in a wide range of arrow weight in ready to hunt conditions with a random bow from the company while magazine test is done only at 9 gpp and with a naked string with a bow send to the tester in the purpose of magazine review :campfire:
Blacky
I know your work and respect it.
My assesment was 10 gr variation leads to 1 to 1,5 fps variation in hunting bows. So 100 gr leads to 10 to 15 fps.
So 300 gr lead to 30 to 45 fps variation right? that what show the graphs. Bur these 300 gr on bows in the 50# range represent 6 unit in gpp variation. If you take a 60#+ bow, variation on those 300 gr will be on 5 or less unit of gpp, thus the "loss of speed" will go down , closer to the 100 gr/ 10 fps.
If you look to average "hunting arrow weight" thus 500 to 650 gr the variation is right on 150 gr/ more or less 20 fps and if you look close to the 10 to 12 gpp range (wich is the sweet spot for dynamic efficiency) those 100 gr go for less than 15 fps in speed variation at least for 3 of the bows.
if i put the graphs for light R/D LB or straight LB in the 10 to 13 gpp you will go more for 100 gr/ 10 fps speed variation.
Our testing protocol is more orientate towards hunting, maybe that is why our result are a bit different.
Glad to share some bow physics with you.
Regards
Guys thanks for the posts. I love technical info. Both methods were just shown to be valid and that they correlate well. I have noticed during personal experimentation that 10 fps makes little difference in point of impact @ 20 yards. 30 yards is a different story. This info will help put a lot of speculation to rest. Blacky, it must be nice to have all the latest bows to test and shoot on a regular basis. Lots of folks here would love to have that opportunity.
Man I wish my release and accuracy were good enough to notice the difference.
:banghead:
:D
QuoteOriginally posted by MCNSC:
I learned this the hard way. If you are happy with your bow don't shoot it thru a chrono. ;)
X 2
This stuff'll make ya crazy!?
Know a guy w an ACS longbow. Most tests I see those are 200 fps at 9 gpp. He gets 180 fps. Is the diff him, the bow, string, arrows, or chrony? Beats me.
IMO, a lot of variation in a lot of fingers out there is dragging some stuff down. And funky cronys.
Sometimes I see what Blacky sees (50g = 10 fps), and sometimes I see the other (50g = 5 fps).
I have a bow that does one w a Dacron string and the other w a Fast Flight Plus string...
I just don't think this stuff is as repeatable w bows, strings, and arrows as it is w guns and ammo. Fingers on a string make way more difference than fingers on a trigger. Way more variation in the former than the latter IMO.