Ultra EFOC results in Buffalo arrow

[Troy Breeding]

#5225

My current setup has been working fine. A Beman Bowhunter shaft in 300 def. 31.250″ long with 250 gr. up front. FOC is 20% and so far has been fine for me.

Well I deside to try for Ultra EFOC.

I knew I would have to shorten the shaft to get this so I desided to start by shortening the shaft to 30.5″. Thats only 3/4″ shorter than my normal, what could that hurt?

Once the insert was set I started by switching to a 315gr point (190gr glue on with 125gr steel adpt.). After afew test shots I could see it was still too stiff.

Now I pull out some of my 20gr GT weights and installed acouple. Take afew shots, but still too stiff. Add acouple more, better but still stiff. I kept adding weights and shooting until the arrow hit the up and down line on the target every shot.

After that I desided to add up everything to see what I had.

Well,,,,, 315gr point, 21gr insert, and 12 ea. 20gr GT brass weights. Add in the shaft and nock, three 4″ feathers (after fletching) and grand total weight came out to 888grs. The FOC is 30.3% so if I understand the range right I now have an ULTRA EFOC Buffalo arrow. 🙂 🙂 :-0

Guess I’ll be starting over and this time I’ll start with a 31.25 shaft,add weight until it shoots weak, and if the foc isn’t what I want I’ll trim alittle off the rear.

Troy

[Troy Breeding]

#38523

Too add to this I want to point out that I broke one of my cardinal rules for arrow tuning….:roll:

NEVER CUT MORE THAN 1/2″ AT A TIME…..:shock:

I paid for this by ending up with more overall arrow weight than I wanted…….:evil::twisted:

Troy

[Ed Ashby]

#38535

Troy, that should make one heck of a buffalo arrow. Now all you need is more bull … buffalo. Did it kinda thump your target when it hit? Sounds like you might not need to build your arrow plate out after all.

When the tuning gets ‘close’ I shorten only 5mm at a time; about 1/5 inch. It’s sometimes amazing how much difference just that 5mm makes. 😯

Ed

[Troy Breeding]

#38579

Ed,

Trust me when I say I knew better…..
Guess I had a brain F@%#. My current setup braeshafts great so I figure I’d have to cut and try so many times it would take all afternoon. Wanting to see results with the work ended up costing me a shaft and still about half a day.

I do have a question for you. Why is the point or broadhead length not counted in the FOC formula. The reason I ask is when I started the test I really had a 250gr point on. To get the shaft to shoot clean I had 15ea. 20gr weights behind the insert. Thinking that using that many weight might be resulting in a false stiffing of the shaft I removed 3 weight and went to the 315 point. Basically the same weight setup. However the balance point changed. With the 250 point and weights my FOC was 29.5% when I switched to the 315 point and removed 3 weights it went to 30.3%. The 250 point is 1.375 ” from the point to the shoulder. The 315 point is 1.875″. Moving the weight out that much upped my FOC.

Troy

[Ed Ashby]

#38678

Troy Breeding wrote: My current setup braeshafts great

Troy, I see you’re still trying to keep abreast of the subject. Your setup BRAeshafts great? I’ll bet it does!

That shift in the measured FOC is understandable. You moved more of the weight further forward, increasing the measured FOC. I use the shaft length to measure FOC, rather than overall arrow length, simply because it is the AMO standard measurement, and has been in use longer than the ‘overall arrow length method’. I’m doing a copy and paste from the Prologue to the 2007 Updates on your question about measure FOC that discusses FOC and the two measurement methods but, in a nutshell, either of the methods only provide us with a relative number, not the arrow’s true FOC.

From: Prologue to the 2007 Updates:

What’s the “correct way” to measure my arrow’s FOC? The AMO Standard FOC measurement uses shaft-length; ignoring insert, taper and tip (broadhead) length. The other commonly used formula employs the arrow’s overall length; including the insert, taper and tip. Which is “correct”? Neither. True FOC is based on the center of pressure. We merely simulate the CP location in both formulas. The AMO formula was adopted as ‘standard’ merely because, between the two commonly used formulas it uses a simulation point nearer the actual CP location for most commonly used target arrows during flight through air.

Just as it is with static spine, the FOC ‘number’ we use is definitive of absolutely nothing about our arrow’s flight. The commonly used static spine and FOC ‘numbers’ merely allow us to make a relative comparison of one arrow to another; nothing more. For example, static spine measures relative stiffness of a shaft; how much it flexes when a weight of specified mass is suspended mid-way between two shaft-supporting points; which are located a specified distance apart. Everything about the measurement is relative, not absolute.

Static spine tells you nothing at all about an arrow’s dynamic spine – how it will react when you shoot it off your individual bow. If you doubt that, perfectly tune an arrow from a true center-shot bow and then measure its static spine on your spine tester. Now take that same arrow and shoot it from a non-center-shot bow (one with a peg rest – no arrow shelf at all) of equal draw weight. What happens? The arrow will shoot massively strong-spine. The arrow hasn’t changed; the launch-force and power stroke are the same; and the shaft’s static spine hasn’t changed. However, the shaft’s dynamic spine is now no longer anywhere close to correct, and it no longer shoots where you’re aiming.

All static-spine indicates is the relative stiffness of the shaft. What it does do is provide you a reference point. This helps whenever you need to find a stiffer or softer spine in order to get your arrow to shoot well from your bow. This is all it does; nothing else. It merely allows you to compare shafts relative to each other, so you can tell which one is ‘stiffer’ and which one is ‘weaker’. Static spine’s ‘relativity’ is precisely why it’s necessary to tune your arrow to your bow in order to get correct arrow flight.

No static measurement or calculation contends with the myriad variables encountered when you shoot an arrow from your bow. This is why, besides charts, Easton publishes 35 instructional pages on selecting ‘the right arrow’ after you’ve used their ‘static-spine’ charts to find a ‘starting place’. No chart provides a magic number saying, “Pick me. I’m the right one!”

Commonly used FOC measurements are exactly the same; they are relative. Neither formula is “correct”, nor is either “wrong”. Each serves its purpose equally well; providing a reference point. As long as you know which formula was applied to a given arrow to determine its ‘relative FOC’, you can duplicate results. If you prefer, you can re-measure and state the arrow’s FOC in the other format; that’s perfectly alright. It still provides you a ‘relative reference’.

For practical applications, either commonly used FOC formula works equally well. Just remain aware that neither genuinely tells you anything at all that’s ‘precise’ about an arrow’s true FOC. However, for a given arrow design, when our ‘commonly measured’ FOC goes up the true FOC also goes up; but the amount we’ve ‘measured’ won’t indicate the actual amount of change in true FOC. The single most important thing to remember is that the ‘relative measurement’ method you use should always be stated, so everyone is “reading off the same page” when making comparisons, or trying to duplicate results.

Ed

[Troy Breeding]

#38744

Dang,,, I hope you know you have caused me to read more in the past few days than I have in the past two years.:shock::roll:

Troy

[Ed Ashby]

#38751

See what you been missing, Troy? If you hadn’t moved out of the South I’d probably still been stopping by every year to fill you in on the latest research and tank up on all the questions and comments you always came up with, so I’d have new things to think about and test. I’ve sure missed those annual visit with both you and Rod.

Ed

[Ed Ashby]

#38841

Troy, how was the trajectory of the 888 grain, Ultra-EFOC arrow, as compared to a similar weight hickory shaft?

Shooting some similarly heavy, tuned arrows that were IDENTICAL in every aspect except their degree of FOC (and a very slight difference in shaft length) I was seeing a marked difference in trajectory. One arrow was EFOC (27%) and one Normal FOC (12%).

I did the testing at 40 meters (about 44 yards) and the EFOC arrow was impacting (group center) 10 to 12 inches higher than the Normal FOC arrow. I was using a bit more poundage that you shoot and was wondering if you could notice any difference in trajectory with your lighter draw weight on that heavy an arrow.

Ed

[Troy Breeding]

#38903

Ed,

You exactly what I found, it was unreal. I’ve shot too many heavy weight arrows and watched them drop like rocks. This arrow didn’t have that much difference to my normal arrows.

You know Rod taught me how to shoot gap. When I shot my normal gap for 20yds. the UEFOC arrow might have dropped 2″ at most. Had I been using one of my old tapered hickorys it would have dropped 10″.

I’m going to try again tomarrow. This time I’m going to start with a full length shaft, the 315 point and maybe 80grs behind the insert. I’m also going to order some of the 100gr brass inserts that will fit the Bowhunter shafts. I think going that route will move the weight as far forward as I will be able to get it. I may not get the UEFOC, but a super high EFOC will work for now.

Troy

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