Chronograph Readings

[Rik]

Originally Posted by Phil Hodgins

Rik

It is 27" to the centre of the button with 1" beyond it, so the arrow tip is just behind the front edge of the riser window.

Phil

Okay, so your draw length is 28.75".
It's measured to the pivot point (generally the part of the grip furthest from the string - tends to be below the middle of the rear button hole) + 1.75".
27 inches would be your "draw length to the pivot point".

This tends to confuse people when they're trying to guess their draw weight from the limb markings as "38@28" is measured to 1.75" beyond the button, so they end up under estimating. But be aware that some manufacturers do it a little differently (Yamaha used to weigh at 26" to the pivot point, so 27.75", when comparing to a Hoyt).

[Big Boy Blue]

Rik

The draw length you are talking about is what called the AMO draw length if I understand it correctly. Whats interesting is that when I put this info into AA the 1913 shaft is far to weak and the optimum spine is a 1916 Plat Plus.

However as I have said for me shooting both arrows reveals the 1913 tunes fine but the 1916 is far to stiff and i cannot get the bare shafts to tune.

I am confused or what !!!!!

What I am building up to is I am going to buy some ACE's for the coming outdoor season and I want to get them right as they cost a fair bit more than a set of XX75.

Phil

[Huffy]

Reading this thread a question about how accurate are the Chronographs that are available.
For instance would a change in bracing height show up in a different reading?

Thanks, Mark

[Big Boy Blue]

I have not tried it but I did try a 28" 1914 spine arrow which is a little heavier than the 1913, the chronograph was reading 4-5fps less. I would guess that you could use a chronograph to find the optimum brace height as you could look for the value that gives the greatest fps.

Phil

[cliveanne]

I've nowt against using a chrono' , but I still think " A fast miss is still a miss" why worry about the speed of the arrow?

This may seem like a jibe, honest, it isn't. Just my thoughts.

[Little Miss Purple]

yes, I see where you are coming from CA, if it's in the gold - who cares how fast it travelled to get there??? Is the emphasis on speed an issue due to how much effect a bad shot will have on the arrow??

[Big Boy Blue]

A faster arrow has a reduced flight time to the target and thus less time in the air for external influences to alter is trajectory. This becomes more important as distance increases and at the furtherst distances it can turn a hit into a miss.
A faster arrow also has a flatter trajectory which helps were your sight mark is.

Phil

[Rik]

Originally Posted by Huffy

Reading this thread a question about how accurate are the Chronographs that are available.
For instance would a change in bracing height show up in a different reading?

Thanks, Mark

It does on the "light powered" chronos. I can't comment on the radar ones. My chrono seems to read consistently down to 1fps. I did some checking on BH effects one evening and found that increasing the BH by just under 1cm decreased the speed by 5 fps. But we're probably talking about +- 1fps error in that (big percentage). I didn't have enough time to do any more detailed investigations, as there was a queue for the chrono...

Originally Posted by Phil

I would guess that you could use a chronograph to find the optimum brace height as you could look for the value that gives the greatest fps.

I've heard that suggested before but I don't believe it will work. The BH with the highest fps, will be the lowest one you try. You get more speed with a lower BH, within reason. The chrono would have to measure accurately to well under 1 fps, for any fine-grained variations to show up within the general trend, and I suspect they would be swamped by the "noise" - variations in the average finger release.

Originally Posted by cliveanne

I've nowt against using a chrono' , but I still think " A fast miss is still a miss" why worry about the speed of the arrow?

Well... the speed can be used an indicator to other things (like checking the match of an arrow with software..., looking for a shaft which behaves differently to the others..., looking for variations in your form...). And there isn't really anything wrong with trying to get as much performance out of your setup as you can. So long as you keep an eye on group sizes while you're doing it. To paraphrase your quote "a big fast group is still a big group"...

[Big Boy Blue]

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I've heard that suggested before but I don't believe it will work. The BH with the highest fps, will be the lowest one you try. You get more speed with a lower BH, within reason. The chrono would have to measure accurately to well under 1 fps, for any fine-grained variations to show up within the general trend, and I suspect they would be swamped by the "noise" - variations in the average finger release.
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Rik

Using a chrono is similar to the method of watching for the highest vertical grouping on the target as you change the BH. This obviously needs the archer to be able to keep the sight in the same location for the duration of the test.

What your looking for is the point were the bow transfer the maximum amount of energy to the arrow and this may not be the lowest BH. At this point the group will be at the highest position on the target, which should equate to the fastest chrono speed. I do agree that in reality the chrono may not be sensitive enough to carry this test.l

[Rik]

Originally Posted by Phil Hodgins

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I've heard that suggested before but I don't believe it will work. The BH with the highest fps, will be the lowest one you try. You get more speed with a lower BH, within reason. The chrono would have to measure accurately to well under 1 fps, for any fine-grained variations to show up within the general trend, and I suspect they would be swamped by the "noise" - variations in the average finger release.
------------

Rik

Using a chrono is similar to the method of watching for the highest vertical grouping on the target as you change the BH. This obviously needs the archer to be able to keep the sight in the same location for the duration of the test.

What your looking for is the point were the bow transfer the maximum amount of energy to the arrow and this may not be the lowest BH. At this point the group will be at the highest position on the target, which should equate to the fastest chrono speed. I do agree that in reality the chrono may not be sensitive enough to carry this test.l

And likewise, unless the archer has a good consistent form, they won't be able to tell whether the variation in the group position on the target is due to the BH or not... What sort of distance would you need to shoot at to detect sub 1fps variations in speed, from the group position? And how big would the difference be, compared to a "reasonable" average group size at that distance...? And if you're doing something like that anyway, why not just look at the group size? That ought to be a better indicator... I would say that speed is, at best, only a secondary indicator of whether the BH is right. Group size is a primary one - you want the best groups you can get!