As a professional bowstring builder it seems that one of the largest misunderstood things in archery is how to measure a traditional bowstring for a longbow or recurve. I would like to take some time to explain what the industry standards are and why they are in place.
Over the past 75 years people like Fred Bear, Earl Hoyt, Howard Hill, Gail Martin and Ben Pearson helped to get the sport of archery to where it is today. During the evolution of archery it was soon realized that some type of standards needed to be in place so that everyone would follow the same guidelines.
It seems that the popularity of compounds and crossbows has left some of these older AMO standards to get forgotten in the shuffle. With traditional archery still as popular as ever it is important for shooters and retailers to understand how to properly determine the correct bowstring length for these bows.
The correct way to measure a traditional bowstring (or any bowstring for that matter) is to place in on ¼” pegs at 100lbs of tension for a period of 20 seconds. You would measure from outside of peg to outside of peg. This measurement would be the correct bowstring length. At 60X Custom Strings we are often questioned on why do you measure at 100lbs and that it makes no sense since the bow is only 50lbs. I can understand the confusion and disbelief but this is why the industry standard of 100lbs of tension is so important. Every bow string material on the market had slightly different characteristics. One of these is how much it will stretch. By measuring every string at the standard of 100lbs it compensates with the different stretch rates and allows everyone to measure the exact same way. A dacron bowstring, for example, can measure up to 1 inch shorter hand tight then it will at the correct tension while a newer material like 8125 may only have a difference of ¼ inch.
AMO specs state that a recurve or longbow should be braced properly with a bowstring that is 3” shorter (under 100lbs of tension) than the AMO length of that bow. Most traditional bows will be labelled around the grip area with the AMO length. A lot of times a customer will see the bow stamped with 68” and assume that is the string length when it is actually the bow length.
If your longbow or recurve isn’t marked with an AMO length you can easily measure your bow to figure out it’s length. To do so you would lay the bow facing down and measure from bowstring groove to bowstring groove across the curve of the bow’s limbs. You do not want to go down into the grip area of the bow but follow the natural line or belly of the bow. This measurement will be your AMO length of the bow.
Now here’s where it can get tricky. I’ve seen several bows that are marked for one length but measure another. The generally means that the bowyer(bow maker) has marked this bow for the specific length so that the correct bow string length will be used. An example would be a bow that measures 57” but is marked at 58AMO would require a 55” string to achieve the correct brace height. This is why it’s always best to measure a current bow string or contact the bow maker when it’s time to order a new bowstring. Most bowstring manufactures will be able to compensate the 100lbs of tension if you tell them your measured length is with the string hand tight.
I hope this article has helped shed some light on how traditional bowstrings are measured and why they are measured that way. As with anything in life there are always exceptions to the rules of thumb but the methods above will work the majority of the time. As always if you’re not sure what to order or have questions don’t hesitate to contact us with any questions at firstname.lastname@example.org Don’t forget to subscribe to our newsletter for more help how to articles and product reviews.