Shooting in and draw weight....

[DD9000]

Ok another rookie question where the answer will probably be something obvious that I should know already but       I don't so here goes.....

I know that I should expect the Draw weight to drop some after a bow has been shot in for a bit.
But how much variance should I expect?

I am seeing around  10 pound difference from before shooting the bow to after shooting for a couple of hours...

If I unstring it and and let it rest for a couple of hours then the weight pops right back up to the initial weight.....

I'm new enough at this that I don't know if this is normal or signs of a problem. Is this something that I should worry about? Or do I just need to curb the paranoia   :D  

-David

[BCWV]

I'm a rookie also so am interested in what the gurus have to say. In my very limited experience, I've lost as little as 2# and as much as 4 on my wood bows but haven't seen the increase you are.  I've only built 7 so far though, using osage, hickory, and a couple boo backed osage and ipe bows.
 What wood are you using and what type of bow?

[DD9000]

BCWV, This has been on a oak board bow.
I have only had it out shooting 3 times around 100 shots through it each time over a couple of hours.
So it may be something that just needs more time to settle in but don't know what I don't know so to speak      Only made two of them so far...


-David

[Nicon]

Another rookie here. Could it be a stretchy string?
I have a similar problem with brace height. After about an hour of shooting my brace height is about 1/2" lower then when i started. After it has been unstrung and "cooled down" the brace height is back at high. The string is 14 strand dacron flemish and has been shot over 1000x. Is this kind of stretching normal?
Lower brace height should lower the poundage as well. Right?

[John Scifres]

I have never had that kind of change.  Are you shooting outdoors in humid conditions and then putting it back in a low humidity condition afterwards while it is unstrung.  The only thing I can think of is moisture content changing that would bring that much change back and forth.

[DD9000]

Hmm now that you mention that John, this last time shooting it was raining out. While we are undercover we are outside and it would certainly have high humidity in that case   :p  perhaps that is it...
I happened to have had a scale available at the end of the session last night and weighed it and it was a good 10 under what I got when I checked while making it.
I measured on my scale again when I got home about 30 min after shooting and it had gained back about 5  pounds and then sitting inside unstrung for another hour or so then it was back up to the original weight.
Seems a fast change for humidity but I suppose it would explain it better than anything else at this point.    

I'll be heading out again this weekend       and it is supposed to be warm and dry so I'll see what it does this time as well perhaps..

Thank you for the idea.

-David

[BCWV]

David,
 I'd heard hickory will gain or lose weight due to humidity changes like John said above. That's why I asked what wood it was. I haven't seen a difference with my two hickory bows so far.
 I agree with John, moisture content would be the only thing that makes sense to me.

[BCWV]

I was typing when you were. I'm slow!!

[DD9000]

BCWV, Yep I have read that Hickory is susceptible to weight changes due to humidity as well.   I guess I never really took that to it's logical conclusion    :cool:    that really any wood could probably  have that happen to it in the right circumstance... that and I did not think it would be so rapid.
Curious to see what it does this weekend.

Thanks again for the ideas

-David

[BCWV]

I am too. Let us know how it does.

[Pat B]

Moisture is the first thing I thought of too. Any wood bow will be affected by relative humidity(R/H), some woods more than others. Generally it isn't 10#. A well seasoned stave will make a bow that is less apt to take on that much weight loss. Most of my self bows won't change much unless they are subjected to day after day of high R/H. Even being strung for 5 or 6 hours at a time doesn't affect them much.

[DD9000]

Well the weatherman was a big fat liar this weekend       and I have had more rain and 70% humidity here in the great pacific northwest, so no real way to see if on a dry sunny day the bow would not drop as much weight over a shooting session.

It sure sounds like that is the issue though.
I'll post again when we have a stretch of nice weather again, possibly this coming weekend....


-David

[dfrois]

Are we talking about 10# on a 30# bow, or a 90# bow?What kind of bow: recurve, D/R, longbow? What is the string material? How many strands?

All of these factors may contribute to a (possibly cumulative) loss of weight in the right conditions...it would be easier to figure out what is happening with more info on these areas. Still, 10# sounds like an awful lot...I hope you get to the bottom of this. Perhaps we will all learn something. Good luck!

DF

[DD9000]

dfrois,

I hope to get some dry weather this coming weekend maybe...

In case it does help with some ideas.
The bow is from a red oak board
a 72" tip to tip 71" NtN
40# at 29"
12 strand b55 string
has glued on static recurve tips non bending portion of the tip is probably only about 3 inches.

Given the weather I am guessing all the signs do point to humidity....

-David

[dfrois]

According to TBB, all wood bows lose some weight between the time they are first strung and aftyer being shot for a while. They even recommend that the weight should only be measured after the bow has been strung for a while, and not immediately after stringing it. Besides that, Dacron (which I believe Brownwell B55 is) also stretches after being stressed firstly, which is why people leave new strings under stress for a few hours before using. If you don't, there will be variance during first few hours of use. Nicon may be right, at least for part of the loss.

To isolate the effect of the string, measure the brace height as precisely as poissible, right after stringing and a couple of hours afterwards. Any decrease is due to string stretch. 12 strands is not a lot, being at the thinner end of the "normal" spectrum, but it is surely enough for 40#. Being a long string (71" bow) will have more material to stretch.

Finally, did you do the finish with a moisture-proof product? Bare wood will absorb a lot more moisture than a waxed or varnished piece.

You could always get a moisture meter. There are a few very cheap Chinese ones on ****. Perhaps not very precise, but should report large variances...Good luck. I'm sure many of the members would like to know what you find about this.

DF

[DD9000]

Ok,I have now had the chance for a couple more outings to the range with some very nice weather.
Based on this I really think those who were suggesting humidity as the culprit must be right on.      Or at least it seems to have...  

In the last two outings to the the weight has dropped from the beginning of the session to the end, but only around 5 lbs at most.

Thanks everyone for the ideas. I had read in the TBB that humidity could make a bow loose weight, but as with most things, there is  bit of a difference in how it seems when you read it vs some actual experience with it.

Obviously I need a bit more of the latter vs the former       ...


-David