Bare shaft tuning help

[sjohns4]

I'm shooting a Mathews Feather Light (think '98-'99 era) that I've had since it was brand new. Most if it's life has spent slinging 100 grain 2-blade broadheads at white tails inside 30 yards max just fine.

After a couple years of hunting elk I'm giving the setup some overdue attention. My setup is currently: Cabela's Stalker Extreme 340's, 9.2gpi (or close to it), 30" arrow on 29" draw length, 70# draw weight.

So I played with some heaver tips initially, 250 grain tips (factory aluminum inserts) shoots pretty good. I loose a little trajectory out to 60 but can still keep 20 through 60 pins in a sight housing - I like it.

Figured with heavy tips I'd be under spined, but wanted to test it before ordering new arrows.

Bare shafts hit right with fletched arrows out to about 20 yards. When I move back to ~25 yards the bare shaft takes a hard right and hits about a foot or so right of my fletched arrows. I'm a lefty, so a right bare shaft should mean too stiff an arrow. That didn't make sense. I did a couple shots with 100 grain point too and was still hitting right.

Even with my slow old bow I cant believe I'm over spined with 250 grains up front on a 30" 340 shaft. The rest appears to be in the center shot, and measures 13/16" (my bow is so old couldn't find the published center shot dimension, but that's what Matthews says all their bows are).

Any idea what gives here or what I should try next?

 

[5MilesBack]

I'd go right to BH tuning at 40 or 60 yards with a fixed blade head, since that's the end goal anyway. I like to BS tune just to get close so I don't have to tear up my BH targets as much, but I always finalize with BH tuning at 60 yards.

 

[PMcGee]

Yeah I’d just try your broadheads. You need pretty damn good form with a bare shaft after 20yds. If you’re hitting together at 20yds your broadheads should be close.


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[Zac]

I can't imagine any spine chart says 340 with 250 up front is okay. I would cut those things down to 27.5 range.

 

[Beendare]

I can't imagine any spine chart says 340 with 250 up front is okay. I would cut those things down to 27.5 range.

Agreed^....it sure seems like you are under spined. ...and under spined is bad with BH's.

 

[Jimbob]

For the most part, right and left bare shaft is not affected by spine when you are using a release and compound.

The power stoke of your bow is pushing off to the side of your arrow causing the bare shaft (no fletching to fix the misaligned power stroke) to hit right.

To fix you need to change the power stroke of your bow, shimming cams, twisting yokes, adjusting cable guard or move the rest so the arrow aligns with the power stroke.

 

[Billy Goat]

What rest are you using? Some hide things more than others close range.

As suggested I'd move to broadhead tuning. If you can put your broadheads with your fieldpoints at 60 that's all your ultimately worried about.

 

[sjohns4]

I was thinking the same yo guys are, and the charts are showing my arrow combination is suitable for like 35 pound draw weight. I should be under spined, and was figuring on ordering stiffer spined arrows, but a right bare shaft for a lefty is supposed to mean too much spine, or so I've read. Also sheading 150 grains up front doesn't make that much of a difference.

I'm using a QAD drop away.

I think I'm hearing, said different ways, I might need to look at rest adjustment...and probably the best way is adjusting to get the broadheads grouping with field points....I think it's move the rest towards the broadhead group, right? BUT, if I'm actually way under spined like we all think I am, will this work?

 

[Billy Goat]

I have noticed that heavy tip weight or high foc seems to make it easier to bareshaft tune, except it doesn't tell everything.

Move your broadheads towards your field points with very very small rest adjustments. Make marks where everything is to start and take notes on what you do and the reaction. Don't be afraid to go the wrong way from what you read if the results are positive. Single cam bow correct? I don't know much on those but it should mostly be setting the centershot I believe.

 

[sjohns4]

yep, single cam. I started out to get an idea of how much weight I could shoot before too much of an arch and similarly how under spined I'd be. Is it a reasonable assumption if I get my center shot right with the 340's, a stiffer arrow wont change rest adjustment?

 

[MattB]

I can't imagine any spine chart says 340 with 250 up front is okay. I would cut those things down to 27.5 range.

Yup, way underspined and I don't even think that would do it. I had spine issues with almost that same arrow length/deflection at 71# at a 27.5" DL and with only 150 grs of insert/point weight.

This strikes me as a case where a guy got an idea from reading too much on the internet and now needs to fix something that wasn't previously broken. But FOC......

 

[Billy Goat]

yep, single cam. I started out to get an idea of how much weight I could shoot before too much of an arch and similarly how under spined I'd be. Is it a reasonable assumption if I get my center shot right with the 340's, a stiffer arrow wont change rest adjustment?

If you are happy with the weight/speed you will probably need to change arrow shafts. Going to need a stiffer spine which will be a heavier arrow, then loose point weight. If your going for high foc you will loose some of what you have with your current setup, but that's part of it.

If you actually get your centershot right ( meaning you are getting a good broadhead tune) then it's no point to change spine. Keep in mind that's not screwing on a mechanical and hitting close to your field points at 25 yards. I believe once you start playing with broadheads everything is going to change, and your going to see what is actually going on.

 

[sjohns4]

I was playing with my current arrows because they have the same grains per inch of 300 spine black eagles...so figured at least I could play with head weight and see if my old bow could at least stomach more weight. I like the way the arrows have been flying with the heavy field points. Any guesses though on spine for a heavier point setup though? Most charts I've Googled assume a 100 or 125 grain point. I'm not out for extreme FOC...so far it's just been a side effect. Even with a stiffer spine I think I'll need decently heavy point weight to stay in the current ~550 grain arrow weight.

Yeah, the guy read on the internet heavy arrows penetrate better; an additional 150 grains is noticeable on the target. Guy also wondered why he could only ever shoot 2 blade broadheads. I'll keep my 2 blade broadheads, but shouldn't HAVE to shoot them.

 

[Billy Goat]

Every 25 grains on the tip is around 3# of draw weight if I remember correctly. So a little math and you can figure a calculated draw weight to use.

Can also look at the difference from 100-125 tip and figure a difference. Remember those are starting points to get you in the ballpark.