EFOC-Stu Calculator-Way underspined Arrows...

[dave19113]

Here's a question.... I had planned to use 2219's with 275 up front on my 67# LB. 28" arrows 27" draw, 705 Grs finished. They shot ok but not spectacular. They chrono'ed 153fps. I personally am not into the speed thing but doing the math they only push as much energy as my 52# bow. I ddnt go with a heavier bow to get same results. i could of just saved money and bought more arrows and stuff. According to the calc they should be pretty close and the velocities they are supposed to push should be more like 180fps...

I had some 2018's and Gt3555's for my lighter weight bows and said lemme try. The 2018's have 200 up front, 605grs total, and the GT3555, 275 up front 565gr total. Both arrows well above the 8gpi minimum but are SUPPOSED to be way underspined. Well they both shot light darts, i ddnt get to chrono them but i can just see from shooting them that they are moving much quicker with much less drop at 20yds.

There is the background, now for the question... I read that Fred Bear and many others regularly shot underspined arrows because they did shoot better.... Is they any down falls to it?

And am I doing any unforscene damage?

When you check the GPI you just divide your arrow legnth by total arrow weight including broadhead or just arrow no broadhead?

[Bud B.]

Alot depends on how much off-center your shelf is. The more off-center, the more underspined you should be.

Example;

My Super Grizzly rated 50# @ 28 shoots 30.25 1916 Legacys very well with 100gr tips. I measure 3/16 off center with the strikeplate I have on it.

Same arrow with same tip shoots out of my 65# LB with 7/16 off center shelf shoot just as well.

If I pluck the string I see arrow wiggle, If I have a smooth release I have darts flying.

I'd love to see a super slow motion of the 1916s paradox out of the longbow. It scares me a little to think of shooting underspined wooden arrows out of the LB which is why I shoot 60-65 spined cedars out of it. They do fly rather well out of it though.

All thing being perfect I can see great benefits with the calculator. It definitely can save you some time in tuning. When you start adding in the human factor as well as the type string silencers you may happen to be using and things change for sure.

I guess that's why the shooting form factor on the bottom right is there. If you use the calc and then get a tuned arrow but it doesn't quite match, then entering + or - numbers in the form factor can bring the arrow/bow numbers closer. I tend to be a -2 to -3 on it.

I'm jumping to 2016s as soon as they arrive.

Hope some of my muttering has helped.

Bud

[rraming]

the off center is one item which is "touchy" the other is brace height, there is no option for it and I have one longbow which uses a 7 3/8" brace height and Stu chart is always off on that bow - good program though

[JimB]

GPP is total arrow weight including point divided by poundage at your draw.

I haven't been able to get Stu's calculator but most that have chronoed,say it is off on speeds but most also say it is fairly accurate otherwise.

I think if you work a momentum formula on your setups,you will find that 705 gr arrow has more power than you think.That isn't a heavy arrow for that bow.I shoot arrows that weight out of 50-55#'s.Having said that,I would be more concerned with good arrow flight and whatever works,works,regardless of what the calculator says or what works for someone else.

It is a good idea to bareshaft some arrows,then broadhead tune after setting up via the calculator.

Check out the tuning info at bowmaker.net.It has helped me a lot.

There won't be any damage from 8 GPP arrows.Poor arrow flight will rob a lot of energy and reduce penetration though.A heavier arrow,given perfect arrow flight and all other things being equal,will harness more of your bows energy and usually shoot quieter.Narrower shafts like the 20 diameter aluminums vs 22,would aid a little in penetration also-all other things being equal.

[Doug in MN]

As mentioned above you have to be spot on with the on or off center measurement, 1/16" makes a huge difference

The closer you are to all measurements the better STU's calculator works.

[rastaman]

GPI is arrow weight divided by the length of the arrow. GPP is the total arrow weight divided by poundage at your draw.  

[AKCrazyhorse]

I've had similar results with the EFOC and UFOC set ups.  I've got a beman 500 cut short to 26" shot off a 52lb Centaur (at my draw length) laminated bow.  This arrow sports a 100 grain insert and 300 grain head.  Two different calculators show it way underspinded.  Yet it flies perfectly and the bare shafts and fletched shafts hit together out to 30 yards.  To get it even close in the calculator I have to us a -15 form factor. As I understand it, the lower the number the better the form and release and I can tell you neither my form or my release is THAT good.  Having said that I love Stu's calculator and have found that the arrow weight and FOC measurements are super accurate.

[dave19113]

Thanks all... thats basically the same conclusions I came up with...... I was just more worried about the arrows being too light and damage the bow. the 2018's weigh 605gr @28" so doing the math thats 21.6 GPI? and the GT3555 weigh in @ 535gr @ 28" wich is 19. GPI? Thats why I was asking if I weigh the arrow with BH/Inserts.....

[rastaman]

Dave, your math is correct but i don't understand why you are concerned with grains per inch.  Grains per pound of draw weight is more of a concern.  Most bowyers recommend 9 grains per lb or higher to not void their warranty.  As long as your bow can handle it and the noise is manageable, 8 grains per lb and higher is ok in my opinion for deer sized animals.  Assuming you are drawing approximately 65lbs at your draw length, the 605 grain arrow comes in at 9.3 grains per lb and the 535 grain arrow comes in at 8.23 grains per lb.  Neither should damage your bow, and as long as they shoot great, they should absolutely take care of any animal you are shooting.  
Good luck to you sir!  

[dave19113]

Originally posted by rastaman:
Dave, your math is correct but i don't understand why you are concerned with grains per inch.  Grains per pound of draw weight is more of a concern.  Most bowyers recommend 9 grains per lb or higher to not void their warranty.  As long as your bow can handle it and the noise is manageable, 8 grains per lb and higher is ok in my opinion for deer sized animals.  Assuming you are drawing approximately 65lbs at your draw length, the 605 grain arrow comes in at 9.3 grains per lb and the 535 grain arrow comes in at 8.23 grains per lb.  Neither should damage your bow, and as long as they shoot great, they should absolutely take care of any animal you are shooting.  
Good luck to you sir!      

Thanks... Thats what i was hoping to hear...The % is a lil lower... the bow was built 67# @ 27".... but its still ok with me.....Now I just have to get a deer to stay still long enough...  

[Bjorn]

"I read that Fred Bear and many others regularly shot underspined arrows because they did shoot better..."

Where did you read this and what was the context?

[JimB]

I had to edit my post.I said GPI when it should have been GPP (grains per pound)

[dave19113]

Originally posted by Bjorn:
"I read that Fred Bear and many others regularly shot underspined arrows because they did shoot better..."

Where did you read this and what was the context?

I was reading an article, I do not remember where, but it stated that he would regularly shoot underspined arrows and that it seemed to work for him. But again, I dont remember where. It just made the point that most ppl shoot arrows that are over spined and that is why so many ppl have problems tuning.

[xtrema312]

I have found a slightly weaker spined arrow to be a little more forgiving with field tips to shoot, but not with a braodhead on it.  If your broadhead shoots great you got what you need.  With very high or better yet EFOC I find you hit a point where you can shoot a real weak dynamic spined arrow of 320-30# under spined even with braodheads.  A bare shaft will fly ugly as all get out, but with feathers it works on some bows.  I have a Fire Fly that loves a weak EFOC arrow, but none of my other bows will shoot them.  GPI is only useful in figuring the arrow weight.  Different bows have different performance levels.  You may very well find you light bow outperforms your heavy bow in speed if both are shooting the same GPP arrow.  You may also be short drawings the heavy bow a little and losing some performance.  That can happen.

[Hookeye]

OK, somebody mentioned 20/64ths vs 22/64ths diamater possibly making a difference in penetration (all else equal I assume).

How can that small amount make for a difference, when:

The broadhead cuts a substantially larger hole ahead of the shaft.

The tissue is compromised and the shaft will be passing through in a fraction of a second (elasticity of the tissue substantially reduced by trauma).

On a 2 blade there may be some drag issue along the edge of the ferrule kinda perpendicular to the blades, and if using a large shaft with a stepped insert from BH to shaft then I could see some loading at that small transition but.........

there's lubricity in the wound fluids and the tissue again has been compromised.

I don't think shaft diamater to be an issue as far as friction is concerned (maybe not what was said- but I've heard/seen it mentioned elsewhere so am asking). There may be something to do with shaft flex at impact, maybe allowing for some sideloading of a BH during travel through the target medium.

But that is a flex issue, influenced by diameter but not fully governed by it.

Got into this discussion with a Six Sigma Blackbelt........and he said "well they pull out easier". Ugh.

The arrow has stopped travel, the tissue has closed/laid against the shaft.......yeah a smaller shaft might pull out easier (again there may be a flex issue when pulling it out or attempting to). But there I think BH blade angle at the back etc. to make for way more of an issue when backing one out, than shaft D.

I just never bought into the smaller is better deal, with shafts, based on the often touted friction argument.

But then I almost always blow through my deer  

[dave19113]

Originally posted by xtrema312:
I have found a slightly weaker spined arrow to be a little more forgiving with field tips to shoot, but not with a braodhead on it.  If your broadhead shoots great you got what you need.  With very high or better yet EFOC I find you hit a point where you can shoot a real weak dynamic spined arrow of 320-30# under spined even with braodheads.  A bare shaft will fly ugly as all get out, but with feathers it works on some bows.  I have a Fire Fly that loves a weak EFOC arrow, but none of my other bows will shoot them.  GPI is only useful in figuring the arrow weight.  Different bows have different performance levels.  You may very well find you light bow outperforms your heavy bow in speed if both are shooting the same GPP arrow.  You may also be short drawings the heavy bow a little and losing some performance.  That can happen.

Yes... It literaly shoots exact where I point.... I guess Im not gonna complain... I was just a little worried due to its a brand new bow.... And I love it.....

Good luck all....

D

[Manitoba Stickflinger]

The way I see it, is if the arrow is flying well (bareshaft, fletched, and with broadhead) it is not under-spined but the proper spine!....it's the charts that are over spined. Just like the comment about Fred using underspined arrows.....says who??? If they are working for him then they are the proper spine....not under-spined. Saying "under" or "over" spined is saying it's not the right spine for the bow....if they are tuning they ARE the right spine.....Just my 2 cents...Ryan

[rainman]

It makes perfect sense that Fred Bear shot underspined arrows, he shot off of his knuckle, therefore did not shoot a bow with a cut in sight window.  The arrow therefore had to bend around the handle of the bow.

[Bud B.]

Fred Bear's recurves still had cut-in risers. His index finger was the shelf. The shelf was rasped down so far his hand took over supporting the arrow.

 

[Friend]

Stu's calculator is a great tool. My experience with upper EFOC arrows shows no correlation between dynamic spine and arrow dynamic spine required.

I do use the calc for calculating FOC and total arrow weight and for referencing dynamic spines that worked before on EFOC set-ups.