Changing strike plate to affect pt. of impact?

[NYRON]

Hi All:

Here's my situation. Recently I switched from split finger to three fingers under. When shooting split finger I shot the same arrow (Carbonwood 3000 cut to 29" w/ 250 grains up front) from 3 TD longbows with the exact same point of impact. The bows are Striker 56# @ 27," Kota 57# @ 27," and Boss 54# @ 27." I could switch from bow to bow without any change in accuracy.

Now that I have switched to 3 under, the Striker continues to hit dead on, but the Kota consistently shoots 6 inches to the left while the Boss hits just to the right of my aiming point at 20 yards. This isn't a form problem as it doesn't occur with the Striker and the symptom is different with the Kota versus the Boss. Also, bare shafts from the Kota and Boss fly perfectly, suggesting spine isn't a major issue either.

I suspect that the problem is related to how deep the shelf is cut on each bow. The Striker is cut to center, but the Kota and Boss are not. My goal is to make each bow shoot to the same point of impact with the same arrow. The Striker is my "go to" bow so I'd rather not mess with it.

But, I'm willing to experiment with the other two. Although it seems counter intuitive, I read somewhere that hitting left of your aiming point can be remedied by building the strike plate out to change the point of oscillation as the arrow passes through the sight window.

Finally on to my question...can anyone tell me how changing strike plate thickness might affect the arrow's point of impact?

Thanks for your help.

Ron

[McDave]

I have a Das Dalaa that initially grouped to the left of my other bows.  It has a moveable strike plate, and I was able to move it a little to the right and correct the problem.  Even after I moved the strike plate a little to the right, the arrow tip was still a little left of centershot, so maybe they had the strike plate adjusted too far out when I bought it.  But you're probably not going to be able to move the strike plate to the right on your bow.  You could try moving it to the left and see what happens; maybe it will be counterintuitive like you said.  You can probably build it out to the left temporarily with some cardboard or something to see what happens.

Mathematically, a 1/8" movement of the strike plate should move your group about 3" at 20 yards, which is about the amount of correction I needed to make on my Dalaa.  Of course, moving the strike plate also changes the effective spine of the arrow, as you note, so it's more complicated than a simple mathematical proportion.

[katman]

McDave is right on. For a right hander add to the strike plate will move impact to the left and require a less stiff arrow. The closer to center shot the wider range of spine the bow will shoot well, so it makes sense your Striker is still dead on.

Also changing to three under may shorten your draw a little, decreasing power. How each bow is tillered would also come into play. Most like to shoot three under with an even tiller and the slight positive tiller for split.

I know when I change between split and three under I must adjust the arrow spine, especially when I string walk.

[NYRON]

McDave and Katman:

Thanks for your input. I appreciate the sound advice.

This morning I played around with the Kota a bit. I temporarily taped a piece of foam about 1/8" thick to the side plate. My shots moved about 3" further to the left, exacerbating my problem.

Then, I tried adding point weight (75 grains) to decrease dynamic arrow spine. It had no effect. I consistently shot 3" to the left at 10 yards.

I'm going to experiment with the brace height. If I rasie the brace height enough I might be able to weaken the dynamic spine a bit.

Thanks again.

Ron

[Vintage Shooter]

Hi Nyron,

I shoot 3 under and I've had the same problem. Point of impact was consistently to the left.  Groups were great, just not where I was looking.  Here's a trick that worked for me.  A long-time traditional shooter showed this to me a few years ago.  He explained that the problem could be solved not so much by changing the thickness of the strike plate, but by the nature of the actual material used for the strike plate.  For my problem, I needed a softer strike plate to absorb some of the energy that wanted to push the arrow off of the strike plate and cause impact to go to the left.  He pulled off both my velcro rest and calf hair strike plate and replaced them with a soft, fairly thick, spongy rug rest.  It's the ones that you can cut and then peel the back off of to expose the adhesive.  He did this for both the rest and strike plate.  It wasn't as pretty, but my arrows instantly shifted to the right and somewhat lower; exactly where I was looking.  Maybe using a soft rug rest for your strike plate will help you, it worked for me.  Best of luck.

[katman]

You would have to thin the strike plate to move the arrow right. Can't cut the riser and can only get so thin on the strike plate. I suspect the tiller may be different on the bows.

If you want all the bows to hit the same and continue to shoot three under you may need to add to the strike plate for the Striker and Boss to move the arrow left to align with the  Kota. Of course you will have to retune.