Compound Bow Dry firing- why the destruction?!

Kernowlad

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I do like my compound archery a lot but there are definitely dangers with the bows that "normal" archery doesn't suffer from; one being the dreaded dry firing.
I've seen the damage it can do when a fellow (very good) archer just forgot to load an arrow into his lovely new ?1200 bow. Wrecked the strings, trashed a cam module - ?200 of damage. But even more alarmingly, it could have caused a nasty injury (there was just a small cut).
So why does the very small resistance of an arrow "work" fine but without it the whole bow self destructs?
If I can learn a bit more about the mechanics of them, I will hopefully have a little more confidence in my kit.

One thing that happened last night on an otherwise quite successful shoot - the arrow came off the rest a few times. All but one I managed to replace it with my finger but on one it REALLY came off and balanced on my left (I'm right handed) wrist causing mild panic as I stood there not wanting an arrow to go in some random direction if I drew down too quick (I had to hold it a while and got someone to replace it while I held it at full draw - not ideal!). It doesn't happen often at all but it would be good to have a better plan. My indoor arrows also happen to be extra sharp.
 

bimble

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compound bows need arrows in the 5-5.5gr per pound (of draw weight) so that when they are shot there isn't too much energy for the system to dissipate. When you forget to put that arrow in all the energy that is taken by the arrow (which when you think a 400gr arrow is accelerated up to +280fps in a couple of feet) is kept by the bow.... and lost by sending bits everywhere!
 

KidCurry

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As Bimble said, the stored energy of the bow at full draw is transferred to the arrow at release. It a bit like punching a pillow, the pillow absorbs the energy of the punch. Punch a brick wall and the energy is absorbed back into the hand resulting in a broken hand.
 

geoffretired

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I always say that the best way to find out just how much energy goes into the arrow, is to try this little exercise.
Take one of your arrows and stand with it at a foot or so from the boss. Then, in a dagger stabbing manner, see how far you can stab the arrow into the boss.
1/4 " perhaps.
Then see how far the bow can send it into the same boss.
 
D

Deleted member 7654

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If you do a back of a fag packet calculation you'll find that the acceleration of the arrow is over 300g (as in 300 times the acceleration due to gravity) thus the "resistance" (inertia) of a 1 ounce arrow is equivalent to almost 19 lb weight (8.5 kg if you are metric).
Remove that resistance and predictably all hell breaks loose.
Del
 
D

Deleted member 7654

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I always say that the best way to find out just how much energy goes into the arrow, is to try this little exercise.
Take one of your arrows and stand with it at a foot or so from the boss. Then, in a dagger stabbing manner, see how far you can stab the arrow into the boss.
1/4 " perhaps.
Then see how far the bow can send it into the same boss.
No... don't stab your boss! .... he means the targetty thingy.
Del
 

Rik

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Supporter
"Small resistance of the arrow..."
Think of it this way: if you have 70% efficiency (a figure often quoted for a recurve), only 30% of the energy stays in the bow on a normal shot. So, on a dry fire, more than 3 times as much energy is left to dissipate. Looked at that way, it's not so surprising it can do damage. I bet a compound is more efficient than a recurve, which makes the end result relatively worse...
 

jerryRTD

Well-known member
I do like my compound archery a lot but there are definitely dangers with the bows that "normal" archery doesn't suffer from; one being the dreaded dry firing.
I've seen the damage it can do when a fellow (very good) archer just forgot to load an arrow into his lovely new ?1200 bow. Wrecked the strings, trashed a cam module - ?200 of damage. But even more alarmingly, it could have caused a nasty injury (there was just a small cut).
So why does the very small resistance of an arrow "work" fine but without it the whole bow self destructs?
If I can learn a bit more about the mechanics of them, I will hopefully have a little more confidence in my kit.
.
It's times like that when a good shot routine is so necessary when I go through my shot routine and I get to the bit concerning the arrow, I do not just nock it. I check the vanes, point and nock orientation. I nock the arrow and check the fit of the nock on the string. Because I carry out these checks I am far, far less likely to forget to fit the arrow to the string.I even went as far as not having a c.o.c.k. fletch on my arrows so I have to pay attention to the arrow to nock it the right way up.
 
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Kernowlad

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It's times like that when a good shot routine is so necessary when I go through my shot routine and I get to the bit concerning the arrow, I do not just nock it. I check the vanes, point and nock orientation. I nock the arrow and check the fit of the nock on the string. Because I carry out these checks I am far, far less likely to forget to fit the arrow to the string.I even went as far as not having a c.o.c.k. fletch on my arrows so I have to pay attention to the arrow to nock it the right way up.
I'm not actually that worried about an accidental dry fire - I've never been even close to forgetting an arrow. Just worrying to see the destruction caused.
What I did learn last night is that PSE cams aren't very strong and that some bows (Hoyt, possibly mine) are much stronger and can handle a dry fire. Point Shoot Explode appears to be a moniker not entirely unfair to the brand... However I still don't want to accidentally do one.

I've reduced my draw weight a bit and practised man draw downs- far more confident now. Sadly that didn't translate to more accurate last night....!
 

Rik

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Recurve dry fires can be reasonably impressive too...
I saw someone have their string snap from one, but only after the string loop had carved two parallel notches about 6 inches or so down the limbs. The sharp edges cut the string, in the end...
 

bimble

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This is always an amusing video to watch... and wince at... Hoyt's 1,500 dry fire testing...

[video=youtube;_uobdhZ28U4]https://www.youtube.com/watch?v=_uobdhZ28U4[/video]
 

KidCurry

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Over the last 30 years I think I have seen around 8 or 9 dry releases. I have not seen anyone hurt by them. I do think, however, the greatest risk is if the peep is not tied in.
 

Kernowlad

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Impressive Hoyt vid.
I'm not likely to dry fire but I does remind you that you are using something pretty potent that needs a lot of respect.
 

Kernowlad

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Yes, a compound is a spring under enormous tension, even at rest.
Even though I know it's fine, I still found myself being veeeery careful when undoing the draw length bolts yesterday...! Wasn't entirely comfortable until all four where completely tight again.
 

geoffretired

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I still get nervous when I press a compound. I remember an expression.... " I know some old electricians and some bold electricians, but I don't know any old, bold electricians." It is good to go carefully; but not so frightened we forget something vital.
 
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