Why is this happening?

[ksbowman]

I have two bows with draw weights within one pound.Both by the same bowyer,both risers center cut,in esscence indentical bows.One shoots 3" to the left of the other at 15 yards shooting the same arrows.The brace hieght,nock hieght,all setup the same.I'm pulling out what little hair I have left.Does anyone have any ideas why this is happening?I have even moved up and down spine wieght of shafts to no avail.  Thanks,  Ben

[McDave]

Have you actually measured the draw weight, or are you just going by what's marked on the bow?

Are they identical bows, or different model bows that happen to have the same stats?  For example, if I had a longbow braced at 7", and a recurve braced at 8 1/2", both center cut (but not cut past center) I would expect the longbow to shoot to the left of the recurve, since when the arrow leaves the string, the arrow fired from the longbow will be angled somewhat more to the left than the arrow fired from the recurve.

If the bows are made out of different material, even if they measure the same weight, it will be found that one bow will be more efficient than the other (deliver more energy to the arrow).  This could be noticed by shooting the same bare shaft from each bow, and noticing that the bare shaft from one bow impacts the target at a slightly different angle than the other bow.

For example, I have an older model 65# BW and a newer model 60# BW.  The newer model has bamboo in the limbs, and is more efficient than the older model.  They both happen to shoot the same bare shaft the same, as close as I can tell.  Which is nice, since I can practice with the same arrow with the 65# bow that I hunt with in the 60# bow, and expect the trajectories to be the same.  It's sort of the opposite of your problem, but illustrates the point.

I'm sure you wouldn't even notice the difference if it were the only bow you were shooting, since you would just adjust.  I had a similar situation with my DAS bow that wanted to shoot to the right of my other bows.  Fortunately, I could adjust the arrow rest to eliminate that problem.  Otherwise, I don't think I would be happy having bows that wouldn't hit in the same right/left orientation.

[ksbowman]

McDave,I worded that wrong the bows are cut past center and the arrows are on center.I put both bows on a scale earlier and the both scaled correctly,because like you I thought maybe they were seperated by more than a pound in wieght.Yes,they are the same model bow but,they are not the same in manufactured years.Shooting them thier speed seems the same,but I don't have a chrono.They are recurves and your explaination of one being more efficient than the other bears merit as one is a single carbon and one regular glass.The trajectories seem the same out to 40 yards,the bows shoot the same except the left to right and doesn't seem to change much out to the longer yardage,as I would expect it to magnify.  Thanks, Ben

[McDave]

I expect that the bows do have different efficiencies.  When you shoot a fletched arrow, it will flex differently coming off each bow.  However, because of the fletching, it will recover quickly and proceed downrange on a more or less parallel course.  You could test this by shooting bare shafts from each bow.  I would expect that if my theory is correct, they would continue to diverge.

If my theory is correct, you could solve the problem by separately tuning arrows for each bow (using a stiffer arrow in the more efficient bow), which would then impact together.

[Rod Jenkins]

Even with the best bows available, there can be quite a bit of difference in performance, between bows built to the exact same specs......all wood isn't the same!

[Jacko]

Have you bare shaft tuned your arrows for both bows . Also perhaps each bow needs individual tuning in brace height , nocking point etc due to minor tiller differances . Could also be some minor differance in the shape of each bows grips . regards Perry

[Orion]

It's my underestanding that one piece of carbon will add about 5-8 fps to a bow's speed, compared to glass.  That's about equivalent to a 2-3# difference in draw weight.  On bows cut past center, you can and probably should overspine considerably, about 15-20# or so.  If you're right on the edge of a weak spine, that could accentuate the difference between them.  If you're already considerably overspined, I'm at a loss to explain the discrepancy.

[ksbowman]

I had two different brands of bow quivers on.One {a good well known quiver] evidently was causing torque while shooting it I took it off and it cured shooting left on that bow.Put the other brand quiver on and they both shoot the same.  Thanks,  Ben