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Pac8541

Tuning questions

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I know this topic comes up a lot but I can't seem to get my head working this evening. My field points are hitting really well; consistent and accurate and they seem to be flying well. When I swap them for broadheads of the same weight everything hits about 2" left. They are 2-bladed one piece heads and thought wind planing first. So I tried different orientations of the blade to fletching to see if that might make a difference. Nope. Then I tried moving the arrow rest 1/32" right. This worked and brought the BH's into the center, but guess what happened to my field points? Yeah, 2" right. Here are my arrow specs:

 

ACC 340's 26.5" long.

175gr field points.

175gr VPA 2-blade BH.

Firenocks

3.6" Flex Fletch vanes, 3-fletch, right helical

Total arrow weight: 509gr.

 

I just picked up a dozen FMJs from a buddy. He builds them really heavy and shoots a 100gr head with them. These things are shooting the same hole but with a slightly different BH (vented). Still a 2-blade though. Literally no difference from FP to BH. Arrow specs on that set:

 

FMJ 340s, 26.5" long.

155gr steel and brass inserts at the front.

100gr field points.

100gr Silverflame vented BH.

Standard nocks.

Small shield-type vanes, maybe AAE, 3-fletch right helical.

Total arrow weight: 583gr

 

Shooting a BT Allegiance, QAD drop away rest, with a release. Is it the vented heads not catching any wind? Is there a way to fix this? I've got quite a bit invested in the ACCs and would like to stick with the VPAs at that head weight but I guess I could change things up. Plus, the vented Silverflames hiss all the way to the tgt which I don't care for.

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Have you paper tuned the bow? That always seems to me to the best easiest way to make sure your bow is indeed tuned and shooting arrows straight. Could be a tuning issue. Also could be you torquing the bow. The field tips will recover quickly making it not as noticeable. But with the broad heads might be an issue. Also could be that the broad head/arrow/fletching combo just doesn't like each other. Just off the top of me head thoughts 😀

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Dave: it is maxed out, I'll give that a try tomorrow.

 

Becker: I paper tuned it last spring with these same arrows and it came out fine, or so I thought. I was kind of leaning that way though, thinking I'd have to re-do it just to make sure. I don't believe I'm torquing the bow but I guess it could be happening. I've spent a lot of time paying close attention to my bow hand, string contact with my face, playing with stabilizer weight and distribution... I figure I've got a pretty good handle on torque. But, it is possible.

 

My son has this slo-mo video feature on his phone. Its quite awesome. And it makes identifying things like torque and arrow flight much easier. I'll have him record a few shots next time he's over.

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A lot can change from last spring. Just you shooting form changes day in and day out. I would throw up some paper just to make sure. Just an easy way to make sure.

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If you haven't checked tune since last year my bet is string stretch or something like that....also I had some of the same issues with a non vented head...much more sucesptible to torque and speed..

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Good call, both of you. I'll paper tune it again just to be sure. There's no reason with the speeds I'm not shooting that I should get planing like this at 20 yds. I mean, I don't understand all the physics of it but I'm shooting a heavy arrow with an older bow and getting chronographed speeds of around 260fps. According to OT2, I'm not over/underspined. In fact, this very combination yields a dynamic spine of 338; dang near exactly on the spine rating for this shaft. FOC is just a hair under 16%. I tested 3 different vanes before settling on these.

 

Yeah, I gotta paper tune and see what's going on.

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actually it's more likely to be cable stretch then string stretch but the other thing you need to look at is if you move the rest you are no longer shooting through the center and moving the rest is the absolutely wrong way to tune.broadhead if your timing of your cams are off and your rest is not set at center then everything else will falter from there. think of it this way if you're shooting a rifle and you're shooting different rounds and one round is heading to the left you don't move your barrel to the left to make compensation

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actually it's more likely to be cable stretch then string stretch but the other thing you need to look at is if you move the rest you are no longer shooting through the center and moving the rest is the absolutely wrong way to tune.broadhead if your timing of your cams are off and your rest is not set at center then everything else will falter from there. think of it this way if you're shooting a rifle and you're shooting different rounds and one round is heading to the left you don't move your barrel to the left to make compensation

This makes sense to me because I am a rifle shooter by profession. However, based on all the broadhead tuning articles and blogs and pro tips I've read, moving the rest to tune broadheads seems to be a perfectly acceptable and correct way of doing things. I completely agree with the rifle barrel analogy but we don't have the ability to move the rifle barrel; therefore, every adjustment to the rifle that we do to zero it must be done through the sights. If that results in running out of windage and elevation travel in the sights or scope then we look at other ways to bring that adjustment back into its center.

 

Cable stretch may be the culprit or the string.... Its all one unit with the Bowtech. I'll start with examining my cams to make sure they're turning over together then paper tune. Once I get clean holes there I'll start fiddling with my sight. Might try a lighter weight BH too but the 150s are shooting left also and going lighter than that starts messing with shaft spine. :angry:

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You sir are correct, according to the pro's not the actual technicians who make a living doing just this. For some reason to me it makes no sense to make the arrow come out of the bow on a crooked path rather than straight down the center of the power stroke when basic aerodynamics and physics say that differently shaped objects should not fly the same. If you put vanes that are flexible on the back of an arrow to help steer the arrow what makes you think a rigid wing style object on the front won't steer it? If you are truly center shot and not torquing the bow and everything is in tune then common sense says adjust your sight since you probably won't be shooting much field points during the hunt. I understand the columns about this stuff are written by the pro's but usually (not always) do these guys actually do very little work on the bow themselves. The guy's who engineered the bow spent a ton of time trying to make it shoot properly and taking it out of their specs rarely makes it better yet simply disguises the real issue.

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Not at all, didn't read it that way and it never occurred to me. I appreciate the feedback. The reality of this is, it serves me right for neglecting my bow for so long.

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Move the arrow rest to get your BH and FP to group, then adjust your sights to zero the group back on point of aim. Make small simple moves with your rest, no more than 1/8" if hitting to the right move left, if hitting to the left, move right. Your objective is to get BH and FP to group. Not to move your BH group to your point of aim. Then once you have the "best group" with both BH and FP you then adjust your sight to get you group hitting on your point of aim. Good luck, and remember to keep it simple.

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So why throw your bow out of tune(providing it is in tune) so your broadhead hits where your sight is? You now have a poor flying arrow that will hit its mark instead of a well tuned arrow that will fly like a dart instead of having a "fishtail take-off". If your bow shoots a "bullethole" and your bheads are off a little than your field points move your pins. Not every paper tuned bow will group the same. A lot will. 3 blades catching air are way different than a field point. Not to mention FOC, arrow spine and length,wrist torque,poor release,too short of brace height cuz you gotta have all that speed,cam lean,string stretch,timing issue,wrong draw length, vane clearance on cables and rest,not centering your peep on sight ring.not level. Someone chime in on what I missed please.

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You will search and find a thousand different answers on the best way to tune.

Here is my take...

Paper tune is not perfect.

1. it doesn't take into count distance from paper etc.. A perfect tear at 10 feet may not be perfect at 7 or 12.

2. String/cable stretch does and will happen over time, and will cause a change in paper tear, hence arrow flight.

Broad head or walk back tuning or other types of tune may not be perfect either.

 

All tuning is dependent on grip/torque/spine etc..Even the best archers in the world don't have perfect form in every situation, (none that I know of, some better than others )

 

What I do: (real world application for those of us not perfect)

1. Get as close to center shot as possible

2. paper tune at various distances and get the "best" tear I can.

3. walk back method (sometimes)

4. Broad head tune with a fixed, mechanical and field tip, only making very small adjustments. IMO if your broad heads and field tips hit together, your grip/torque is being accounted for and arrows are flying true.

A broad head will exacerbate any imperfections and tuning issues. especially a fixed broad head.

 

By this time I can shoot any broad head, for the most part, and have it impact the same as my field tips up to 100 yards.. (judging on my abilities as a shooter)

In my experience anything over 90-100 yards broad heads will tend to shoot slightly lower than field tips. Mostly due to a decrease in aerodynamics on ANY broad head from field tip.

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