I find apologists for weak traditional or selfbow performance extrodinarily exasperating. There is no excuse for below par performance, none. "If I wanted a fast bow I'd shoot a compound" is just about as assinine as my kids argument "I don't have to do my homework, she never even looks at it." That said, if YOU make a bow and it shots, then you deserve enormous credit, and you should be very proud. My point is, this is not a contest, or about any individual, eg. "you," that the bow you prefer or that you made shoots slower than others, it's simply an unbiased assessment.
On to the topic, unbiased assessment is often almost impossible to accomplish. It's not sufficient to simply use a chrono, for example. How you shoot a bow can make a dramatic difference, easily enough to mask the bows real performance, either to the "good" side or bad. So, at a minimum one needs a chrono or two, and a machine to shoot the bow. Now I realize almost nobody goes to that much effort, but some do and I think it's important to focus upon what they learn or observe, to the exclusion of all the other noise on the topic.
I'm not an expert, but I'll try to relay accurately what I believe, what I've learned and experienced directly, and what I've read. Some of this actually comes directly from Mojam I, some from the Walk-the-talks boys, some from one of Norbert Mulhaney's assessments posts at AL Adcocks site.
A common and practical way to compare bows accross a wide range of draw weight is to settle upon a standard. "AMO" or now perhaps ATA standard has been 60#, 540g (9 gpp) @ 30". Most find that a little on the extreme side and have settled on a measure of an arrow weighing 10 grains at 28". That's I think where the Mojam paradigm, 50# bow, 500g arrow, 150 fps thing comes from. Unfortunately folks are real particular about regulating power stroke, or string mass which are also very relevant. I like to use 21" power stroke (28" draw and 7" brace) as a reasonable standard, and low stretch string whether linen or other.
Given the standard conditions offered above, and assuming ideal moisture content of say 7% (a most frequently overlooked factor) a selfbow, no sinew just straight selfbow ought to shoot 10 grains per pound at 150 fps, 165 would be excellent, and I suppose one could conjecture 135 would be the other end of that "bell curve."
Since everybody shoots a slightly different setup than the standard, rule of thumb adjustments can be made. For example, each inch of power stroke is worth about 6 or 7 fps. Each 1 gpp (60# bow, 540 grain arrow vs 600 grain arrow) is worth about 12 fps. My experience has been 1% of MC is worth about 5 fps depending. Linen or low stretch string about 5 to 10 fps.
Aside from the obvious, good materials, sound design (including low mass, stiff outer limbs), effective moisture control, good limb timing or "tiller", the one thing I have found which will improve cast perhaps more than any other aspect is to always stay within the elastic limits of the material, throughout the entire building process. Also, or more or less being redundant, this also includes (actually excludes) the practice needlessly overworking the bow, so called "working in" tillering adjustments. I accept the fact the this concept is beyond many folks ability to concieve, or as likely reluctance to accept, but the difference can be amazing, like another 10 fps on a typical project. Once, or if, you put your mind to it, you'll find it not trivial to get 10 fps, or even 5 fps, over "standard." cast.
I'll close by admitting my first MoJam, which I think was Mojam II actually, I had the same experience. Mine was more about the look of the bows, rather than the cast, but the cast too. I don't recall ever being as embarassed, ashamed even, of my work when I saw what could be done with natural material. That I could make a bow that would not break with repeated use was, I first thought, a real accomplishment. I was proud as all getout. I had no idea this was, on the grander scale of reality, not even a relevant measure. Not to belittle the craft, a newbies first bow is an enormous accomplishment, something one should be proud of. But with rare exceptions, there is always room for improvement upon that first project, usually lots and lots of room for improvement.
I honestly don't think most selfbowyers really have anything to be worried about. 135 fps is not a "bad" number, but I'd imagine pretty common. Given another inch of draw, a decent string, a point of moisture content, etc. that could easily equate to the "standard" 150 fps or more.
Topic: Selfbows and efficiency (Read 456 times)
