Can anyone explain what IBO and AMO means?
That you put in AMO you are pointing to standards of fps once used by bow manufacturers. They don't use either.... Well, you can get AMO, but have to call the factory.
So more or less for speed shooters;
IBO is basically the rule set forth by the IBO, International Bowhunters Organization. Okay, 30" of draw, 70 pounds of draw weight and a arrow weighing 350 grs (5 grs per pound of draw weight).
More or less heavy bowhunter equipment;
AMO was formerly the Archery Manufacturers Association and now the Archery Trade Association. Here, the draw length is 30" with draw weight of 60 pounds and a 540 gr arrow.
Today the IBO has been replaced and is confusing. Now called, ATA.
ATA fps is to be derived from real numbers. Okay, IBO pounds could be that of up to 82 pounds so long as 5 grs. per pound of draw weight was used.
Read link and I'll see what else I can find.
Last edited by SonnyThomas; 01-28-2011 at 06:21 AM.
IBO is what bows wish they could shoot, and AMO is closer to what they will shoot. lol Or you could use Sonny's explanation. lol
exactly ehunter, ibo is for manufacture sales not real life hunting cause once you start rigging out your bow thats when it gets real, not what somebody selling a bow says your bow should shoot. hope im not stepping on toes.::
Manufacturer numbers are real, but we have to think of them as a starting point, not the finished bow set up. I would say these IBO and AMO listings are a starting point. Where would you start being there are some 3 1/2 million archers with whatever different number of bow setups?
Again, I thought the ATA fps listing is confusing. As long as you have 5 grs of arrow weight per pound of draw weight what's the problem? Noted in the link was 82 pounds. So what? I mean, there are factory bow of 80 pound draw weight. Hoyt and others offer 80 pound bows! I know for a fact you can get bows of 100 pounds of draw weight.
If you read the replies of the link you would have read of one person relating of REAL numbers. Well, more people do use a draw weight in the 60 pound range. Next real, real is the average male in the United States. He stands close to 5 foot 10 inches tall - so 70 inches tall which is normally that person's wing span. So 70 - 15 = 55 / 2 = 27 1/2" draw length.
I have a Pearson TX4 with IBO rating of 340 fps. As is it has a 28" draw and maxed out at 62 pounds. I have a loop on the string and nothing else. I used a 314 gr arrow - so 4 grs heavier than allowed IBO spec. It chronograph-ed 310 fps.
Using the below rule of thumb for speed adjustment I came up with the following;
310 + 16 (dw) + 1 + (arrow weight) + 20 (dl) = 347 fps.
And somewhere in here I did the same correction for my Shadowcat and came up with 323 fps. Listed is 320 to 325 fps.
Rule of thumb for speed adjustment;
2 fps / 1 # of Draw Weight
10 fps / 1" of Draw Length
1 fps / 3 grains of arrow weight
1 fps / 3 grains of weight on the string
??? Hutch, no comment?
Well, Hutch, I'm sort of lost. Most bows set up at the factory will reach or exceed the listed IBO. I exampled my Pearson TX4. Actual listing for the TX4 is 340 fps +. At a factory the bow is virtually a bare bow with some type of rest and some type of nocking point. I've heard a single brass nock, string tied nock and no nock at all. Now the ATA surely has something they all agreed to use in testing. If not, X bow maker would be on the Soap Box claiming their competitor was using unfair tactics.
Slip over to the automobile.
A car manufacturer claims X car will do 0 to 60 in X seconds. I won't question that and people except the claim. But then we put four people in the car, use different tires, X brand gasoline and how fast will the car go in the same X seconds? Better yet, when was the last time you heard X car won't do the claimed speed?
So skimming over some bow sites; Hoyt has the ATA thing, Ben Pearson has IBO and Martin doesn't say either way, but lists 70#, 30", 350 gr.
What would be nice is, if someone would come up with a system that showed a bows speed rating with a typical hunting setup. Say 60 & 70# draw ratings with a 350gr & 400gr. arrows respectively, at 27.5 inches. Peep, D-loop, and string silencers. Limbsavers on the bow. Make one universal rest for testing. That would help put an end to, or slow down, all the "Why won't my bow shoot what the factory says", as well as give us all a better idea of what we can actually expect from the bow in a real life situation. Noone I know of hunts or target shoots with a tied on knock, and nothing else.
It would be nice to see more realistic numbers, but I think bow set-ups are as varied as the people shooting them and regardless of how you rate them, there is still going be that....."Why won't my bow shoot what the factory says"
I expect for most bow shooters it's easier for them to check the bow speed than it is anything thing else they do.....including tune their bow.
They just walk in to a bow shop, shoot a few arrows thru the dealers chronograph and are upset that the mfr lied.
No consideration is given to draw length or weight, or arrow weight, accessories on string, bow tune, or even if chrony being used is right or not.
Not to blame the shooter, they may not know any better. I suspect most don't.
Using another car analogy, and one drivers take for granted as true. Again because most don't known any different and typically don't have easy means (or money) to verify it, is mfr claimed engine horse power.
Factories get their engine rating sort like bow mfr's get their IBO rating. Measured at the crank under controlled environmental conditions with no accessories.......add on AC compressor, steering pump, alternator and related belt drag, change altitude and barometric pressure, connect a transmission and drive line, various differential gearing, and by the time you get the horsepower to the road you've loss 18-22% of what is claimed.
Knowing what loses can be expected, maybe that's a way to determine the ballparkish speed a bow may actually shoot. Take maybe 15% right off the top of what is claimed for a hunting bow, and maybe 10% off when set-up as a target bow??
2009 Martin Bengal M2 Pro Cam w/factory STS & CCS.....66lbs, 29" DL, 422gr @ 272fps, Winners Choice string/cable, Trophy Taker drop-away Rest, Scott Release
1996 Martin Firecat XRG Pro Series w/Ultra Sonic wheels.....69lbs, 29" DL, 465gr @ 245fps, w/fingers & Martin leather glove