Broadhead tuning issue

[BringBackThe80s]

Up through pre-season, I've had my bow (Matthews DXT 70 lb, 26.5" draw, 5575/400 spine GT hunters, 100 gn heads) set up to shoot shafts essentially touching at 20, 30, and 40 yds (or a mix of those ranges), and 2" or so at 50 yds. Then, after 16 seasons / 20+ deer using NAP Spitfires, I decided to shoot fixed blade (Magnus black Hornet). They are shooting plenty accurate out to 40 yds (have not tried them at 50 since don't go more than 30 yds on game; most shots are 10-20 yds.)

ISSUE: When I first shot the broadheads, they were grouping 3 inches right of field points at 20 yards, a bit more than that at 30 yards. Changing cock feather orientation and nock tuning had no effect--consistently decent groups, but clearly right of the field points. No, not a an issue with crooked inserts or broadheads.

I thought the issue must be windplaning caused by the arrow leaving the bow with a slight fishtail (point to right, tail to left of line of sight) that quickly corrects when shooting field points.. So I moved my drop-away rest to the left, expecting that would reduce or cure the windplaning--moving both field point and broadhead POI leftward, but reducing the gap between them--so I adjusted sight leftward to compensate for adjustment of the rest. The first adjustment did reduce the gap a bit, so that broadheads were landing to the right ~2" at 20 yds, 3" at 30, and 4" at 40yds. I adjusted 3 more times, though, maxing out adjustment on my sight and nearly maxing out my rest.

So, the broadheads are consistently hitting 3-4" dots at 20, 30, and 40 yards. But field points land 2" left at 20 yds, ~3" left at 30 yds, and 4ish inches left at 40 yards. It's a consistent angular difference, so I could adjust my sight and make field points hit at all ranges and broadheads would land 2", 3", and 4" to the right. Also looking at the arrows sitting on the rest, they are clearly left of centershot in the riser.

QUESTIONS: What is the likely cause(s) of the angular difference in flight of broadheads versus field points?

Would grip-induce torque explain getting tight, consistent accuracy with both field points and with broadheads, but at different POIs?

Can you suggest any solutions to what you think the problem is, so that broadhead groups will have the same POI/POA as field points and mechanicals?

 

[Mighty Mouse]

I would move the rest to 13/16” centershot and try yoke tuning to bring broadheads and field points together. BH right of FP = add twists to left yoke & remove same number of twists from right yoke

Here’s a handy tuning guide that I refer to frequently:

 

[SDHNTR]

Grip torque, face pressure, release torque, or cam lean.

You also could be a bit underspined. Without looking it up, .400 spined arrows and modern bows at 70 lbs are not usually a good mix. Yes, yours are shorter, but I still bet things would work better with a .340.

 

[BringBackThe80s]

I would move the rest to 13/16” centershot and try yoke tuning to bring broadheads and field points together. BH right of FP = add twists to left yoke & remove same number of twists from right yoke

Here’s a handy tuning guide that I refer to frequently:
View attachment 942815
View attachment 942816

Thanks! According to this, I moved the rest in the wrong direction. (facepalm) However, since moving the rest (and matching that adjustment with the sight) did not bring the two groups into alignment, I'm thinking that the rest is a non-issue and I need to put it and the sight back to the correct centershot.

 

[bmart2622]

The rest should have been moved to the right with your 1st adjustment since your bhs were to the right of fps. Id set the bow back the 13/16 centershot and broadhead tune.

 

[BringBackThe80s]

Grip torque, face pressure, release torque, or cam lean.

You also could be a bit underspined. Without looking it up, .400 spined arrows and modern bows at 70 lbs are not usually a good mix. Yes, yours are shorter, but I still bet things would work better with a .340.

Thanks! I think my grip is decent, but despite 40 years of shooting, it's certainly possible some coaching could clean it up. I don't think it's face pressure, since the only place the string touches my face is very lightly on the tip of my nose.

As for release torque, I have no idea. I have used the same Scott release since 2008 (it is the Little Goose head, but with a webbing connection to the wrist strap--like a combination of the two releases pictured below. I have the release trigger bar set very light, but it is a single-jaw release. I don't know how those may factor in.

I had new limbs (warranty repair) and string put on it in 2015 or 2016, and I think Mathews sent new cams with the limbs. Is cam lean something you would adjust through left and right yoke tension?

I bow hunt from now on through gun season, so I haven't wanted to make major changes until January. But at that point I'm already planning to move up to a 340 or 300 spine and increase insert/point weight a bit.

 

[Bump79]

I would move the rest to 13/16” centershot and try yoke tuning to bring broadheads and field points together. BH right of FP = add twists to left yoke & remove same number of twists from right yoke

Here’s a handy tuning guide that I refer to frequently:
View attachment 942815
View attachment 942816

This ^^

I thought the issue must be windplaning caused by the arrow leaving the bow with a slight fishtail (point to right, tail to left of line of sight) that quickly corrects when shooting field points.. So I moved my drop-away rest to the left, expecting that would reduce or cure the windplaning--moving both field point and broadhead POI leftward, but reducing the gap between them

Broadhead right = tail left = move rest right. Or yokes.

Set to center shot - Verify that you're not getting any vane contact and adjust per that chart.

 

[MallardSX2]

You could be torquing your bow some.

I copied my reply on another forum over here and this might help you.

Envision your bow at full draw instead of at rest in the below pictures.

Riding true - String running true right down the center of the cam.


Not riding true - Pulled the string over with my thumb at the mid point to show the string not riding true, several degrees to the left.

When someone asks me to help them tune their bow the first thing I do when they draw their bow is I stand behind them and I see what kind of riser hand torque we’re dealing with. I see a lot of people that have weird arrow flight and when they draw their bow, their string looks like it should damn near derail when they touch their release. Then you look at their arrow flight going all whirlybird out through the air. Then the next arrow is fine. Then its a "game of what is happening". A lot of people tune this applied torque out of the bow/arrow during paper tuning. I don't like to do that because unless someone consistent on that torque, its very hard to tune it out of a bow. Really it just boils down to hand torque on your riser. Some of this can bit attributed to a draw length too long or too short. But that's a whole other rabbit hole to go down.

Personally, if I have ANY hand torque when I draw a bow at a shop, I move on. I'm just not willing to fight the fight for the life of the bow. (Most) Bow shops are looking from behind to see the torque but won't bother to mention this to you because they want to sell bows and they will just tune it out for you at the shop and let you go live your life. Which is fine for some/most guys.

I encourage guys to draw their bow, focus on the target and right before they release the arrow to just look up at your top wheel or cam and see how your string is tracking....Obviously this cannot be part of your routine shot sequence, but I think a lot of guys would see just how badly they are torquing their bow and then they wonder why they cannot get fixed blade broadheads to fly worth a crap.

ALSO,

TRY THE FOLLOWING.

Paper tune to a bullet hole and then try a 4 fletch helical.

If that doesn't work, add 25 grains to the front of the arrow and re-tun and try again.

I would be shocked if that doesn't solve your problem.

 

[bmart2622]

Fletching configuration wont change the root of the problem which is the shaft not coming off of the string square and true...fetchings can bandaid it and cover it up but it won't fix it. Bareshaft tuning is a thing for just that reason

 

[SDHNTR]

To clear up some misinformation above.

A broadhead right of fp group is a weak spine reaction. Adding weight to the front would make it worse. Also, the rest should be moved left.

 

[bmart2622]

False, just to clear up any misinformation...you move the rest toward the bh group....broaheads hit LEFT of field points you move the rest LEFT!!!

 

[BringBackThe80s]

To clear up some misinformation above.

A broadhead right of fp group is a weak spine reaction. Adding weight to the front would make it worse. ...

It's what the bow shop set me up with 17 years ago and I didn't realize at the time what a light arrow that was. This summer is the first time I started looking at different arrow builds. Since I mainly hunt close cover from a treestand where I can laser distances to trail crossings before deer come through, I would rather shoot a heavier arrow to dampen sound and increase energy on target.

 

[BringBackThe80s]

Fletching configuration wont change the root of the problem which is the shaft not coming off of the string square and true...fetchings can bandaid it and cover it up but it won't fix it. Bareshaft tuning is a thing for just that reason

Agreed. I'm shooting AAE Max Stealth 3-fletched with 6 degree helical. That's a lot of helical with a pretty large vane and a fairly small broadhead.

 

[Mighty Mouse]

Is cam lean something you would adjust through left and right yoke tension?

Yes. On your particular bow, there’s only a yoke around the upper “cam” (it’s actually an idler wheel not truly a cam). Adjusting the lengths of the yoke legs (via twisting) adjusts the tension placed on the cam/wheel axle and alters the lean of the cam/wheel. Cam/wheel lean affects the path traveled by the string (in the horizontal plane) during the shot.

The goal of tuning is to get the nocking point at full draw (A), the nocking point at brace (B), and the point of contact between the rest and arrow (C) all lined up. If points A, B, and C are all aligned, the arrow will leave the bow flying true and broadheads will land alongside field points (assuming no vane contact or grip torque). Yoke tuning is a means of adjusting points A and B in the horizontal plane.

 

[SDHNTR]

I’m just gonna leave this here for those of you who want to argue with Easton.

 

[SDHNTR]

It's what the bow shop set me up with 17 years ago and I didn't realize at the time what a light arrow that was. This summer is the first time I started looking at different arrow builds. Since I mainly hunt close cover from a treestand where I can laser distances to trail crossings before deer come through, I would rather shoot a heavier arrow to dampen sound and increase energy on target.

That’s all fine, but keep in mind, the weight of the arrow and the spine deflection (stiffness) are two different things.

 

[Mighty Mouse]

Yeah, I suspect spine may be the biggest factor.

It's what the bow shop set me up with 17 years ago and I didn't realize at the time what a light arrow that was. This summer is the first time I started looking at different arrow builds. Since I mainly hunt close cover from a treestand where I can laser distances to trail crossings before deer come through, I would rather shoot a heavier arrow to dampen sound and increase energy on target.

400 spine may be weak, stiff, or perfect depending on how you built that arrow. You’re shooting a slow (by today’s standards) bow at short draw length. Unless you’re using an extra heavy insert and/or cut your arrows way longer than necessary, I think you should be able to make 400 spine work.