about how long should my GT 55/75's be at 57#@28"?

[ozy clint]

hi guys, i'm having fits trying to tune my bob lee takedown curve.
i'm using GT55/75's, 250gr point, 100gr insert, 2" 2117 footing. my draw length is about 26.5"-27" AMO. arrow weight is at 630-650gr depending on length of arrow.
riser is cut 3/16" past center as far as i'm aware and i have a velcro side plate.
string is 8 strand D97.
just when i think it's tuned the next day i go out and shoot and they fly awful. still hit the target but awful flight.
i played with nock point recently and that helped. i'm at 1/2" above square now and i shoot split fingered.

just wondering what your similar setup is and what is the length of the arrow?

[JohnnyWayne]

Clint I shoot AD Trads out of my #57@28 64" Bob Lee takedown longbow cut to 30" with 150 grains up front and they fly awesome. Draw length is 29" and I cut my arrows to 30". Shoot split finger and use regular old strings. I also have a #53@28 62" Bob Lee takedown longbow that I shoot AD Trad Lites cut the same but with 125 grains up front. What's funny is I also have some beman ics bowhunter 400 spines with 150 up front that seem to fly good out of both of the aforementioned bows cut pretty much the same as long as I do my release right and don't pluck the string.

I try to keep my brace heights as recommended in the following chart:

     

Hope this helps some  

[mahantango]

How long are the shafts now? That 2" footing will effectively shorten them, drastically stiffening the spine.

[JimB]

Ozy,this may not help but when I shot 5575's from recurves 52-55# and cut to 30",the most weight I could get up front was about 200 grs.For me at least,and that much weight up front,they would be way weak and no amount of cutting would overcome that much front end weight.

I have used 7595's on those same bows,cut to 30" and 400 grs total in front.Those,in black shaft,make a 700 gr arrow.The weights listed are at my actual draw of 29".If I shot heavier bow weight,I would definitely need stiffer shafts.

Cutting your 5575's as short as you can stand would help but I'm not sure that would be enough.You might try just one and see.I always test with point weight before I cut anything,even if it is a point weight I don't want to use,just to make sure I'm going the right direction.

I would be very curious to see if you would get different results if you tried a 100 gr point? I know that isn't the weight you want but it would tell you if your current shafts are too weak for the front end weight you want.Hope that makes sense.Good luck with it.Don't give up.

Clint, according to Stu's calculator, those arrows would have to be cut about 25 3/4" with that much front end weight (which would be too short for you). You might have to go to a 75/95 to make it work with that much weight on the front.

Bisch

[JimB]

Stu's calculator doesn't work as well on setups with that much front end weight and always seems to show that the arrows are too weak when they actually tune well.I've seen this and others have mentioned it as well.I hadn't worked Ozy's numbers on the calculator so hearing that,maybe a 27.5" arrow would work?Might be worth a try at least.

Originally posted by JimB:
Stu's calculator doesn't work as well on setups with that much front end weight and always seems to show that the arrows are too weak when they actually tune well.I've seen this and others have mentioned it as well.I hadn't worked Ozy's numbers on the calculator so hearing that,maybe a 27.5" arrow would work?Might be worth a try at least.

Thanks for that bit of info, Jim. I have never tried that much weight up front.I did not know that.

Bisch

[ozy clint]

THANKS GUYS! i think you have confirmed my suspicsions.
i've been shooting arrows about 31" long with good flight SOMETIMES but i knew something wasn't right. i tried some shorter shafts that are 29 1/2" long and that has made a big difference. like manhantango said the footing will have the effect of shortening the shaft. so i'm at about what you guys reckon with around a 28" arrow.

cheers guys.

[tex-archer]

I am shooting a 61# longbow with 55/75s cut to 28 1/4" with 270 grains of total weight up front. Stu's calculator show them to be way underspined but they fly great. I would suggest you start with the calculator and just keep adding weight up front until you get good flight.

[ozzyshane]

Clint you are way under spined you will need to build your centre shot out to 0 at a min to shoot EFOC Thanks Shane

[Fanto]

Clint,

I spent the day cursing at GTs also.

I did however crack the riddle of the internal footing. All i did was drill out the back of a 50gr GT weight with a 4.5mm drill. I cut a 6" piece of 6mm dowel, then ground the first 10mm down to 4.5mm did, so it fits inside. i glued it in, then cut a slot so i can remove it with a long, flat blade screwdriver without taking off the point.

presto, adjustible internal footings for stiffness.

Regarding your tuning, my bow is 55# and also cut 3/16 past centre.

     Your arrows are more than 25lbs underspined/B]  

what I have found over weeks of tuning is that fletched arrows NEVER show weak. they bounce and hit left, always showing "stiff"
In case you haven't already, try the setup Stu's calculator recommends. I bet you it bareshafts perfect. for you it would be to build strike plate out to centre and drop to 100gr point. (at 30" shaft" )

 When i built my plate out the shafts tuned with more weight and or length than before, and the groups improved, as well as arrow flight. my 5575s are 29.5 and can only handle 220gr up front assuming cut to centre. this is still marginal.


cheers

[ozy clint]

well i can't work it out. i've had them flying great with the same point weight on the same riser with 54# and a different set of 57# limbs.
i shoot 75/95's out of my 69# bob lee and they weigh 930gr with more point weight.
if 75/95's worked with my 57# setup i'd be suprised, though strange things happen.

i can group my bare shafts and BH's really well out to 30m it's just that the BH's don't consistently fly like laser beams. they always seems to tail wag.
i'm sure it's not a form issue cause i'm hitting right where i want to with consistency.

[Fanto]

clint,

7595s fly like darts out of my 55lb bow with 320 up front.

given the same length, a 7595 can be made to behave the same way as a 5575 by adding 100gr to the point. thats it.

Build out your strike plate, won't cost a cent and takes two seconds. a piece of cork and some tape is all that is required for a test. one of the things that happened to me which absolutely blew my mind was that doing this caused my arrows to hit further right than before.

This is quite a complex issue.

 http://www.archersreference.co.uk/download.html

try reading this. in particular on Node Points

cheers

[BRIARS]

If you are getting good bare shaft and fletched field point flight I would say its the broadheads.

I had a problem with snuffers and had to go to change heads. The old bear razorhead, zwicky eskimo and muzzy stinger flew like darts from the same set up.

[ozy clint]

changing centershot seems to make little difference for me, infact just about everything i change doesn't seem to change anything.

[xtrema312]

I think you are way under spine with all that length and weight.  Probably getting double flex or something that is support critical of form amd draw length.

Do some cutting. Something like 29" to start with a shaft or two and play with some point weights.

Carbon arrows react fast. This allows a lot of false tunes and some people you shoot them at very different stiffness than others do at times. I find more standard point weight to be close for me with Stu's calculator. With high FOC I have to be weaker than the calculator particular with brass inserts that move weight back.  I don't think footing shafts does that much to stiffen the shaft. You bend that last couple inches little if any plus it adds weight to the end.

[Fanto]

Clint

then the other thing that makes my arrows fly horribly but doesn't really affect accuracy much is nocking point height.

what height are you running?

[ozy clint]

yes the nocking point made a big difference. i tried everywhere between 3/8" to over 3/4".
i'm sure spine is the problem.

[LookMomNoSights]

Shoot that 5575 at 29.5 inches.  You have WAY too much weight up front.....seriously....try a TOTAL point weight between 200 and 225.   200 may show a barely noticeable touch stiff,  but most likely right on

[LookMomNoSights]

How much would it cost to send a few arrows over your way Ozy Clint (say 2 or 3)?  As I have a few dozen of the arrows Ive mentioned above....  
Be nice if I could just send you a couple you could try straight away without the hassle......I havent been shooting that shaft lately and honestly may be a while before I do again............