Well, how should you measure a bow's length? Is it the un-strung length as the crow flies, do you follow the curve of the limbs, should it be strung?

AMO stands for the Archery Manufacturers Organization. It created a set of standards for things such as defining bow length. When people give a length of a bow in inches they almost always mean AMO bow length. AMO bow length is the length of the string plus 3 inches. So a 66 inch AMO bow is supposed to take a 63 inch string. But, some people sell strings by "AMO" length rather than actual length, so your AMO 66 inch bow takes an AMO 66 inch string (actual length 63 inches). And, not all bows take a string exactly 3 inches less than the printed bow length. And some bows, especially English Longbows, are measured at their un-strung length.

The Archery Manufacturers Organization is now called the Archery Trade Association.

 

amo on recurves is 4" shorter than actual, longbows are 3", some of my Pearsons take a string 5" shorter than amo

 

amo on recurves is 4" shorter than actual, longbows are 3"

I've heard this figure before, and it seems to be true for some makers. Can anybody cite a source for this standard? It isn't in the published AMO Standards FIELD PUBLICATION FP-3 2000, which rickstix cited and which states:

AMO CONVENTIONAL
BOW LENGTH STANDARD
AMO Bow Length Standard is designated to be three inches longer than AMO
Bow String Master that braces bow at proper String or Brace Height. Bow String

There is nothing about 4 inches for recurve and 3 inches for longbow.

 

Yup…well confusion certainly is understandable and depending on what you read/hear can really make a mess of it ‘cause it’s often more like trying to speak from the other person’s perspective in order to keep explanations brief.

The following links may help to clear things up. And if I can translate what’s quoted below, before you get there…what you get is that the standard for measurement of a bow's length will actually be 3” more than the length of string (under tension) it takes to bring the bow to manufacturer’s recommended brace height.

http://www.texasarchery.org/Documents/AMO/AMOStandards.pdf

AMO Standards Committee
FIELD PUBLICATION FP-3
2000

Page 3
AMO CONVENTIONAL BOW LENGTH STANDARD

“AMO Bow Length Standard is designated to be three inches longer than AMO
Bow String Master that braces bow at proper String or Brace Height. Bow String
Master will carry only the bow length designation. Example: A Bow String
Master designated as AMO 66” (bow length) will have an actual length under
tension of 63”.”

http://www.bowhunting.net/artman/publish/TailorMaidMeasuring.shtml

Happy reading…Shoot straight, Rick.

 

The 4" figure is a holdover from the days before AMO standards were set. At that time many, if not most, of the recurves took a string 4" shorter than the bow (measured along the contour). In fact at that time there were several bows that took strings 5" shorter which would give brace heights in the neighborhood of 10". The old Hoyt Pro Medalist is one that comes to mind. However with modern materials virtually all of the recurves manufactured today take strings about 3" shorter than their AMO length. Longbows on the other hand typically always took strings just about 3" shorter. However, like all rules, there are exceptions to the above.

 

Thanks. I can't find out if AMO/ATA standards have been changed--well, I could, but I don't feel like paying the price. The standards are no longer free to look at. They cost $30 to non-members. And they aren't standards anymore. When it was the AMO, there was a Standards Committee that issued standards. The new by-laws of the now ATA specifically prohibits the creation of "standards". Instead of a standards committee, the ATA has a "technical" committee that creates "guidelines"--which are not available free on line the way the old standard are.

 

LOL…yup, I always use AMO standards from the texasarchery site because ATA would be too much of a hassle…besides, I have 3 dozen or more bows that have been around before ATA was hatched so the AMO standards are still applicable. IMO, do I think any of the rules have changed regarding longbows and recurves…honestly no, and I’d have trouble fathoming a reason why. (Can’t forget ATA has to “create guidelines” because the largest sector of the archery industry “must” sustain itself on "yearly innovation".)

“I'm not getting what you are saying, Rick. The AMO Standard is that a bow should be marked at 3 inches longer than the optimum string length. Therefore, a 66 inch AMO bow should take a 63 inch string (based on a non-stretchable "master string" standard).”

Generally, yes…except it’s not what “the bow takes” that produces the resulting “pseudo bow length”…the matter is string/brace height-driven…it’s what length bow the string takes. (Not my rules!) Also, please consider that the same rule covers more than just one recurve configuration plus longbows, which used to have lower brace heights…so longbows and slightly-recurved fall closer to the 3” specified.

“It sounds to me that you are saying that if one measures a recurve with a flexible tape measure, following the curves of the bow, then the string should be about 4 inches shorter than that non-AMO measurement--which you would only use if the bow didn't have a marked AMO measurement.”

If the bow is unmarked then I will typically proceed as you've mentioned. With a Bear, Wing, Hoyt, Damon Howatt or any of the larger producers of bows, if unmarked I would simply know that “close to” 58 inches is AMO 58”, "close to" 60 is AMO 60” etc. What works for me and many others in the real world is if the bow is well-recurved and says AMO 66" I will make a 62" string.

Unless the bow is a real mongrel the same approximation also works but it could be relatively useless information unless one intends on marking the bow. BTW, if you wondered why string makers might ask for the length of the old string, plus what was the resultant brace height…we’ve just about covered the answer. Take Care, Rick.

High Plains...What was really cool about Herters and how they dealt with this was that many of their bows had the string length given in their emblem/logo. Somebody recognized how confusing this was at the time and how confusing it would be down the road. Rick.

 

wow.. i really didn't know that there was so much to this.. this is really interesting information and it just goes to show that there is a lot that i don't know about this sport..

 

So if I wanted to get a new 58" string for my Samick Sage (62" bow), would I need to get a 58"AMO or a 62"AMO? Does the AMO base off the bow or string? I've heard the 58" is best but I don't want to accidentally get a stri g that is 4" too short/long...

 

Your Sage takes a 62" amo string, around 58" actual measurement.

(The standard was changed at some time, from 4" to 3" less than the amo length of the bow.)

 

Guys (and gals) -

The AMO STANDARD has always been that the BOW is 3" longer than the actual STRING LENGTH.

The 4" shorter can about due to, well, practicality. With Dacron, the stretch was such that the slightly shorter than expected length usually worked out. IOWs, with vintage bows using Dacron, 4" was a pretty safe bet, except when it wasn't. The "wasn't" past was because either some companies (like Herters) just didn't follow AMO/ATA standards, or they picked and chose which standards they felt like following on a given day (Ben Person was known for that on their intermediate level bows).

Can't speak for all the custom guys out there today, but most mass produced ILF rigs will be pretty darn close with a string 3" shorter than it's AMO length. (For example a 68" bow will take an AMO 68" string, which will be 65" - +/-).

Viper1 out.

 

It's an inexact art to make a string within the exacting standards stated above. Therein lies the frustration.

Brace height comes into play as well, for if you like a fairly high brace height on your bow, you may prefer a shorter string from the get-go. Likewise a lower height beckons a longer string. But this is individual nuance per bow.

Dacron will stretch more than Fast Flight, and if you are making a string for a particular bow in your home shop, you may be able to experiment a bit (translation: make the wrong length at least once!) to find a satisfactory length.

There is also the "twist per inch" ongoing battle (I speak Flemish on this one) where some want minimal twisting and others don't mind quite a bit of twisting. Endless Loop has its own set of preferred rules, as well.

If you are ordering a string from anyone reputable, and specify the nature of your bow, they will more than likely provide you with the proper length. That said, there is a chance that the length will be incorrect ... after all, it is an inexact art - and often at the receiving end for the credit card-wielding archer. Letting them know the type of arrows and nocks used helps them to properly serve a proper strand count to fit. This is also part art and part science, and therefore occasionally frustrating, as well.

Strings are a bit like shoes, and we all know how that process can unfold.

 

I have just come across an older Damon Howatt Coronado bow which is marked AMO 60", so I assume that a new dacron string should be about 56". How do I determine what the brace height should be?

 

And don't forget string length is usually measured under tension for the AMO/ATA standard. A loose Dacron string off the bow is going to be shorter than it is when measured under the standard tension (IIRC, 100 lbs for 20 seconds?). And the standard uses an endless loop string w no twists. Flemish you are winging it since length changes w number of twists.

So that Dacron string might be 4 inches shorter in your hand, 3 inches shorter on the bow. Or not.

So... if the bow maker wants a brace height of 7 inches, and an AMO/ATA Master string gets him that 7 inches at 65 inches, the bow is going to be marked AMO 68 inches regardless of what it measures nock to nock along the curve. An endless loop string marked AMO 68 inches will have an actual length of 65 inches under tension w no twists. If the bow maker wants a higher brace height, he could build a longer bow that gets it w that same 65 inch string, and he will mark the longer bow AMO 68 inches, thoroughly confoosing the guys who are measuring the bow... Have an old Matlock longbow like that. He wanted it to brace higher, so he made it longer and marked it shorter.

Since most bows and shooters have a sweet spot and a brace height range (7 - 8 inches) rather than a set point, there is some wiggle room.

I have several older Bear, Ben Pearson, and Gelco bows from the 50s and 60s. Most have the least amount of noise and vibration w a Dacron string that is 3-4 inches shorter then the marked length of the bow when the string is measured on the bow under tension. My sister has an old Herter's bow from the 60s that says on the bow it takes 57 1/2 inch string. It has the least amount of noise and vibration w an AMO 62 Dacron endless loop string w about 20 twists...

 

Thank you sir. This was very helpful for someone wanting to put together their first bow ;-)

 

Open me

 

Amen Teferi

 

Just went down this rabbit hole a couple months ago. Ordered 2 strings from my maker who I have always had no issues with. The bow is a Bear B mag with #3 limbs. Old riser, new limbs. Brace height was almost 9 1/2. I left it strung overnight, 1/2” change. I run my Bear bows at 7 1/2 - 8” . Turns out the bow likes a string 61 1/2“ long.

 

Always smart to actually measure your bow since AMO was always a voluntary program for manufacturers. Several, as Viper alluded to earlier, didn't follow it...like Herter's and Wing, and a few more. Simple process to measure your bow so you really know what it is. If using Dacron, it's usually 4" shorter, or 3 1/2" to be average. With low stretch the 3" seems to work fine on my bows. It's really best to forget AMO since it was made as a manufacturing standard and not necessarily followed. Measure your bows and put your own length on it.

 

Yep. If you measure the bow, then get a string 3" shorter (under tension) than the actual bow length and you should be pretty darn close.