Carbon tuning question - how much does length affect tuning?

[tomsm44]

I have several bows from 42-47# that all shoot great with GT Trad 600s.  The ones I have now are cut to 30".  The bows on the heavier end typically tune up with around 175-200, which gives around 450-475 gr total.  That's about where I want to be on those.  On my 42# bow though, it takes 250 gr up front which is around 525 gr total.  

My question is this.  If I buy some more and leave them at 31", how much lighter can you typically go up front with an extra inch of length.  I'd like to get down to 150-175 gr up front for the 42# bow.  I won't hesitate to hunt with the heavy arrows on the 42# bow, but something lighter would do better for target shooting at longer ranges.  

Also, the 42# is the same model bow as one of the 47# bows that'll be one of my main hunting bows.  If I could get the gpi and speed to match, it would make switching between the two easier for practicing and hunting.

[McDave]

I find that length generally has a greater effect on spine than point weight, so if you go up in length 1", you should be able to reduce point weight quite a bit.

I shoot the same weight range you do, and bare shaft tune all my bow/arrow combinations.  I find that I need quite a bit less point weight to tune than you do.  For example, my 42# target bow tunes well with a GT 600 cut to 29" with a 100 grain point for my 28" draw.  Maybe you draw less than 28"?  I have also found significant differences in tuning between different people shooting similar equipment, which I don't understand, but I guess that's why we tune: to get the arrow that works best for us personally.

If you want to reduce arrow weight for target purposes, you might also consider using a GT Ultralight shaft rather than GT Trad.  The shaft weight is significantly less, which will affect your trajectory as much as point weight will.

[David McLendon]

^^^^^ That...length effects more than point weight.

[ISP 5353]

^^^^What they said!

[the rifleman]

McDave hit the nail on the head.  Carbons generally respond very quickly to small changes in length.  You may check out the heritage 75-- i shoot these out of my 42# Whip.  They are .670 spine.  The GTs shoot very well with 125 field points, but want 150 to tune well enough for broadheads.  The heritage do well w 125.  Im at just over 11gpp and am happy w set up for 3d and whitetIl.

[tomsm44]

Thanks guys.  

Yes, I probably draw closer to 27" than 28".  I'm also shooting primarily vintage bows with Dacron strings and big ole yarn puff silencers.  Not super fast, but they are all whisper quiet.  I also have a newer 42# recurve I picked up for my wife that I have a fast flight string on.  It's noticeably faster and takes a much stiffer arrow to get good bare shaft flight.

Sounds like I could start at 31" and my desired point weight and cut 1/4" off at a time until it's right for the 42# bow.  Worth noting with the 30" 600s is that on the two 47# bows, I can get good bare shaft flight with anywhere from 150-250 gr points by moving my silencers.  With the lighter one, I have to remove the silencers completely to get the 150 and 200 gr points to work ok.

[ozy clint]

i have found that 1" in arrow length equals about 50gr of point weight.

[smokin joe]

Ozy is about right. My 3-D arrows are one inch longer than my hunting arrows and the difference in up-front weight is 50 grains, with my hunting arrows needing the higher point weight to tune the same.