re: Question about broadhead tuning for serious bow shooters

At 20 yards the broadheads are shooting about 4” right of my FP’s

300 spine, 29” arrows with 125 gr points and 100 grain inserts for a TAW of 515 grains

Yes, everything is square and from a lot of stuff I read people say to stay at 13/16” center shot on Mathews. I was just getting conflicted information on chasing FP’s or chasing BH’s when tuning.

4” at 20 yards is quite a bit. That spine shouldn’t give you any problems. Have you shot a bareshaft?

Edit: I also said forget cam lean, but I am curious. are the top and bottom cam both angled toward the cable guard roughly the same amount? if you lay a bareshaft on the cam opposite the cable guard you can see how much they are leaning.

You are absolutely correct about the cam lean, i was just curious. You can’t get it all out with that system and expect it to shoot straight. So the theory of broadhead tuning is that the fixed blades are steering the arrow and if it starts out going in the wrong direction it’ll keep going in that direction. So you want it to launch as straight as possible. A bareshaft does the same thing basically. Like Tomcat, if my bareshafts hit with my field points at 30, I never have to adjust anything.

If it shoots a bareshaft with your fletched field points at distance, I would start to think perhaps you have a bent insert or I’d try a different broadhead of the same model to see if the ferrule is bent or something. Do you feel like your fletched arrows are shooting well?

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They do have some cam lean but on the Mathews’s binary cam system, I was under the assumption you can’t get the cam lean out.

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Correct. Some cam lean will always be there and it’s normal. What matters is getting them timed correctly, which you have if everything is in spec and you can consistently get a good tear bareshaft. Don’t get wrapped up in staying at center shot, make micro adjustments key word being micro.

The part ranch fairy leaves out is you’re fighting an uphill battle shooting field points that create a different FOC than your broadheads. At a certain point you may have to make some accommodation for that, be it with how you build arrows or just shooting broadheads to practice, an underspined arrow pulls right and your longer broadhead arrows have an ever-so-slightly weaker spine, though 4” is excessive and you likely can take some of that out with tinkering that’s been mentioned. At the end of the day if they group, that’s what really matters.

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300 spine, 29” arrows with 125 gr points and 100 grain inserts for a TAW of 515 grains

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If you are shooting 70lbs you are a on the weak side with a 300 spine arrow. Back your draw weight down and see if the groups come together.

I’d recommend using Pinwheel OT2GO and get your arrow setup right before you start swapping top hats and moving your rest.

I shoot mechanicals but still broadhead tune to ensure perfect flight. You don't want bad flight with a mechanical. You will get even worse penetration.

When the OP said matthews and trouble with broadheads I knew this would get wild. For a "top" brand they have shite tuneablity for the average person. They want you in a shop begging for help. That said, trying to tune an underspined arrow with a huge fixed head is a tall order.

OP, your arrow are 29" long. Why? What is your draw length? Like another said, sounds like you are severely underspinded. You have 225 grains up front. At 70# that puts you in 200-250 spine range unless you can get your arrow length down to the 27" range. If you find backing your poundage down pulls them closer together and don't want to give up speed, try cutting your arrows down a 1/4" at a time. This still might not be enough though.

You also said you just put new strings on. I wouldn't worry about tuning it until you have a 100 shots on those strings as whatever you do now will change by the time the string is shot in.

Big arse fixed broadheads need a lot of steering despite coming straight out of the bow. If your form is off at all that thing is gonna plane off. Large stiff vanes in a 4 fletch with 3 degree offset will be a must.

Lastly, have you checked your vane clearance? What rest are you shooting? If it is a QUA or some other cable driven rest your spine problems will be even worse as the arrow is not supported for long enough before leaving the bow. You are better off with a whisker biscuit than a QAD. If you have never tried a limb driven rest you need to. Hamskea and Vapor Trail are the way to go on that end.

Good luck. Just know, sometimes you can't bend the bow to fit the projectile. It needs to be the other way around, and I think that may be where you are.

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custom strings and they are pre stretched

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Every custom string on the market claims to be pre-stretched, and every custom string on the market still stretches. I wouldn’t consider it to be shot in until well over 100 and would definitely recheck everything.