Is there a point in a carbon shaft's length where an over spined shaft starts acting like an under spined shaft? That is to say at some point of over spine the shaft starts kicking off the backplate like a too low nock point starts to indicate a too high nock point because the nock end of the shaft is bouncing off the arrow shelf?

The reason I ask is I was doing some bareshaft tuning with a Carbon Express 250 shaft with an assortment of field tips from 125 to 200 grain. The shaft started 33 inches long and with my 51@28 Pittsley Predator drawn to 29 inches at approx 54 pounds was way under spined. As I shortened the shaft I got to a point where I could change from one weight point to another and the arrow flight and arrow on target point/nock position would change from under to over spine and back depending on the  weight point I used.

So since I plan to use broadheads and field points in the 200 grain range, I cut the shaft another 1/4 inch so the spine indication would be good for the 200 grain point and bam every shot with every point weight now shows under spine.

Am I crazy or has anyone else experienced this? It could be that with all the shooting I could have gotten fatigued and bad form is causing this behavior. I just don't know. I'm gonna give it a rest a few days as see if I get the same results when I'm fresh.

Yea,..I've seen overspined act underspined.You can use some spray white powder like foot or deodorant to spray the shelf area and see where the shaft is hitting.

Thanks R H.

imho....you are overspined....i think the ce 250 would need to be left full length with at least 250 up front...i believe a 30" 150 with 150-200 grains up front would be your ticket..

I'd be inclined to agree with Jacobsladder. I shoot bows in the 60-65# range & I need to leave CX 250s full length with 200gn up front & 100gn inserts to get them flying well. CX shafts seen to be a lot stiffer than you'd expect, especially the Heritage range. 150s would be better suited I think.

Thanks guys. I've got a CX150 and GT 3555 both are showing under spine even at 30" with a 200 grain point. Guess I'll order some heavier points and weight adjusters to see what happens and see if the under spine is really over spine acting like under spine. Better yet if I can find a shop nearby to help with the tuning that might be best. But I can't believe I'm doing something that wrong. But I've been wrong before.    

I would bet a full length CX150 would work well.I never cut carbons to a certin length.I cut 1/4 at a time on one shaft after I make sure it needs to be stiffer.

I just finished barshafting the 150's and I cut them to 29" and the heaviest weight I could go was 175, that showed slightly underspine, 145" looked perfect, 125 also was good to slighty over spined. I wanted to go with more weight but this will do for now.
I shoot a 50# savannah and draw 28"

Well one thing for certain is carbon shaft tuning is a whole lot different than wood or aluminum. Cut 1/4" off a carbon and it changes the spine disproportionately to the amount you cut off.

The full length CX150 and CX250 were showing way  under spine hence the reason I cut them to 31" first then in 1/4" increments till I reached 30". I"ve ordered some additional point weights and weight adjusters and if I can't get the 30" tuned then I'll get new full length test shafts and start over.

Thanks guys.

Ken Beck does an interesting take on tuning in MBB II. It is worth reviewing and may answer some of your questions.

Im having the same thing happen. I have a RER #50@28 and i draw 27 3/4. I tried 3555s trad an camo an 150 heritage.By the time they shot good they were to short for me to fill safe shooting broadheads. I used 125 up to 225 tips. My bow shoots axis 400 standerd inserts 1" footed 2018 an 145 tips,An 250s with 50gr brass inserts an 145 tips the arrows are axis 30 1/4 the 250s 31 1/4. They shoot great

> Ken Beck & MBB II....

don't have a copy but will see if I can get one at the library. My play budget is shot for this month.              

But I've read all the tuning stuff that I can find on the web as well as the sheet Sipsey River sent me so I'm not doing this blind.

longbawl,

Glad someone else saw this behavior too.

RTN

Frank, what kind of arrow plate are you using ?

Joel,

standard velcro that comes with the Predator.

Frank, before I went the new arrow route I'd try a harder plate, leather for example. If that seems to help but doesn't completely cure it, try adding the velcro pad back over the leather

I'll give that a try. I've got some spare leather laying around.

Thanks.

Frank

my tuning stuff(points, pdp weights,etc.) came today. I'll be tuning this weekend and will post an update on what I find good or bad.

well with the addition of a leather backplate with the velcro on top and any combination of point weights 125 grain to 290 grain, 8 gpi weight tubes, pdp weight adjusters, I could never get any indication other than under spine with 30" CX 150, CX 250, GT 3555 or GT 5575 shafts.        

The one constant thing is if I add point weight I get more under spine indication less point weight less under spine. If I add or remove the weight tube I'll get more under spine and less under spine indication. So I'm going to start over and order one full lenght CX 150, CX 250, and CX 350.

If I can't get any favorable results with those then I'm going to say the HECK with carbon shafts and get some Easton XX75 shafts. Never had any problem getting those tuned.

The issue Ken Beck addressed in the video had to do with archers putting too much pressure on the arrow nock when drawing back. The effect was that the shaft would be bent in a downward arc from the rest to the string. When that happens all sorts of unsolvable problems arise. You need someone to watch you draw the bow and sight down the shaft to see if it is straight when you are at full draw.