I've found a good used longbow of 46# draw weight. No string with it. I'm looking for the method of determining string length for making your own strings. I've already got the string materials. Anybody know? Thanks.

The string length for a Longbow is 3" less than the AMO length of the bow.
That is the average but some bows differ.
Some do better with 4" less than AMO.
I would try 3" less at first and see how it performs.


Sag.

Can't say for long bows, but recurve strings are usually 4" shorter than the AMO length of the bow. That being said, when you buy one it should, and usually is marked the same length as the bow, but is made 4" shorter. In other words, if the bow is 62" AMO (marked on the side of the riser) then you get a 62" AMO DACRON string for the bow. I stress Dacron because older bows will not handle newer synthetic materials. There isn't enough stretch when shot which imparts too much shock which can damage or break the limbs.

If nothing is marked on it then try measuring from nock groove to nock groove along the belly of the bow and then subtract either 3" or 4" (it will be up to you to decide which length is better for the bow) and that should be your string length. I use this method on recurves when they don't have a length listed.