Help with brace height of a mongolian bow

If you post a picture of the bow, someone might be able to help. The problem with some bows is that the degree of recurvature of the braced bow can be extreme because the design was based on old photographs where the bows pictured had strings that stretched over years on a wall in a museum. However, if the bowyer has built the bow for that shape, it is possible that the design would be overstressed with a shorter string and a higher brace height.

Thanks Bede,

Here are the pictures.
To help with the sizes and proportions:
- The bow is 58"
- The string is 52"
- I just braced the bow following the idea of 0.5 to 0.75 twists per inch (i choose the 0.5, so it's 26 twists.
- This way the BH is 6 5/8.

I hope someone can help me, and I'm very grateful for your attention

Looking at the angle of the tips, I would think that that is the right brace height. The twist in the string will absorb a small amount of the force of the bow, but not enough to worry about.

Did it come with the string silencers or did you add them because it was too noisy?

If is the string on nominal BH overtwisted, then is the string simply too long.
But i think it looks on this BH fairly good too.

First of all thanks guys. It was a gret help.

The first time I shot, I didn't think it was a noisy, but the after shot was a li'll twangy. That made me think, and worry about the brace height. Actually after the shot it kept vibrating - I thought, godamn... it's musical isntrument! - and I put the silencer (I'm already thinking of reduce the size of them).

I completely agree with you, Jenes, if to reach the nominal BH I had to twist the string that much, the string should be shorter.

This type of bow is a completely different thing to me (asiatic bow) and as it was different about what I was expecting (based on my other bows experience) I thought would be a good idea talk to peolple more experienced.

Thanks a lot. I will be glad if I have the opportunity to help you with something, someday.

Noise in a bow of this shape can have two causes: one is the residual energy left in the bow and the other is a string with too much stretch. In reality, it is the same problem because the stretchy string affects the efficiency of the bow.

Bows with big ears usually operate better with heavy arrows. Manchu and modern Mongol bows are in that category. Depending on the cast of the bow, use the heaviest arrow consistent with the distance you want to shoot. For instance in modern horse archery, the target is close so a heavy arrow is an advantage. On the other hand shooting at 60 or 70 meters would incline you to use a medium weight arrow.

With the string as twisted as you have it, there is a tendency to vibrate like a violin string because it is more springy than a string with fewer twists. When I made a gut string, I had a similar problem, but one caused by the natural resilience of the material. When I shot with it, it sounded like I had plucked a guitar bass string.

There can be some contribution to the problem from the way you hold the bow, but this is usually a very small effect. When I have been standing next to Mongols shooting with traditional bows, I have not noticed much noise, but the arrows for shooting at sur targets are quite heavy.

Lots of amazing informations here, Bede!

If you don't mind I will talk of each one

1. To make the string less stretchy should I think of twist it less (reduce the size of string to keed the same BH)? I can understand the relation of stretchness with the vibration, but the loose the efficiency isn't so obvoius to me. It was a great info.

2. As I shoot on foot the concept of the weight of the arrow. What would be a heavy arrow? I have as reference (ocidental bows of course, and I already understood that some issues are very particular of asian bows) that the minimal weight should be 5 grains per pound of the poundage of the bow at my draw weight. Is it a good reference for a mongol bow? As you said heavy, I mean, how many GPP would be heavy?

3. You asked about the silencers on you last reply. Are they common, or are they worn on mongol/asian bows.? I want to solve this issues to be the more traditional as possible.

Thanks one more time. I'm loving all this informations and I've been checking other threads on the forum. Learning a lot.

Replying to your points, Some answers are easy, but others are more nuanced.

• 1. The string absorbs energy by stretching which is then not available to the arrow. With certain bows, a little stretch is helpful as witnessed in Adam Karpowicz's book about Ottoman Turkish bows. Here he found ultra stiff strings could damage the bow's tips.
  2. On foot, the optimum weight of the arrow is somewhat dependent on the range and the efficiency of the bow. Giving a grains/pound equivalence is really related to the bow it was tested on. I would suggest for short to medium range an arrow in the weight of your equivalent hunting arrow. Field points do this automatically since they are usually matched to current broadhead weights.
  3. Silencers are a twentieth century invention. There was a folk belief that adding weights to a string would improve its efficiency, but this was a misunderstanding. It is possible that some traditional Asian archers are using silencers, but it is a modern innovation. I think they were originally developed for take-down hunting bows that were particularly noisy, but it wouldn't surprise me if American bow hunters invented them even earlier.

I think the best options are:

1. Get another string. Here in Brazil is very hard to get archery stuff, even harder asian archery. For convenience, I think it should be dacron (stretches more protecting the limb tips - some ocidentals bows have the same problems with less strechy materials) and I'll try endless loop and flemish twist to feel and see how it goes.
2 - I'll assume that the BH is something around that you could observe on the earlier posts, I will test with the new strings
3 - Remove the silencers and use the heavier arrows (I have good sets and variety to check. This won't be a problem).

I'm pretty convinced that it will solve the problem, or minimize till the point where some fine tuning will be enough.

Thanks. Excellent tips, one more time Bede!

The only further suggestion I would make if that Flemish twist strings are not a good idea for bows with large ears. They have a little too much stretch.

Bede wrote:

The only further suggestion I would make if that Flemish twist strings are not a good idea for bows with large ears. They have a little too much stretch.

Doesn't it depend on the string material, though? Even if it was dyneema or whatever?

The attachments show 500 server error for me.. ... Would like it if you could upload the pictures to some image hosting site

You can probably get some material that is good for making strings, but not marketed as such, if finding bowstrings is too difficult or expensive. Maybe spectra meant for fishing lines? You should be careful with what knots you use with that type of material, though, and avoid it if your current bowstring isn't FastFlight or similar

I had hand shock with a magyar bow, but heavy arrows, adjusting the nock point, and avoiding techniques of twisting the bow or pushing it forward helped a lot

An endless loop of B-50 (polyester), with the strands pre-stretched to near breaking strength? had little handshock with a 50# magyar with heavy arrows. polyester can act similar to silk; I don't think something super low stretch like polyethylene (dyneema, spectra, fastflight) is really necessary.

An easy way to make a string is to find some braided polyester line that's tough enough and just make knots for the loops. Unless you want to make a jig for making endless loop strings, or learn the Korean method of making strings? (if that works well with spectra/dyneema/etc)

This is the sort of thing Thomas Hard uses for his PVC bows... kind of like a shoelace, but adequate enough IMO

Could search "1/8" Polyester Rope Black"

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Twist in strings can contribute to stretch too. Weirdly all the physical evidence points to the greatest static load is at brace height and it goes down as you draw. I have noticed that the most string breakages I have seen are with Flemish twist strings. Admittedly this is with natural materials. Longbows are much more forgiving.