Balancing weight and speed for UEFOC barely bone threshold arrow

[Kaninmaskwa]

I have read the Ashby reports and all the info I can on setting up arrows for my next bow but I still have a question.
For my own needs I have decided my optimal arrow will be a UEFOC arrow weighing 660gr.
Now the question is what is the minimum speed for this sort of arrow to be effective for standard size water Buffalo?
What about trophy sized Buffalo?
What speed for large Pig?

At this point I'm not interested in debating about just going to higher weight arrows.
What I'm really interested in is the minimum speeds this arrow set up will achieve the required power to be reliable on the mentioned game.
Thanks so much for any insight
Shawnee

[Dr. Ed Ashby]

Shawnee, re-read the 2008 Update, Part 4. The UEFOC (31.4%) arrow testing reported there was for shots on trophy class and large body size Asian buffalo. That arrow had a modest IMPACT velocity of 163 fps at 20 yards, and carried 0.474 Slug-Ft. of impact momentum (and an impact KE of only 38.64 Ft.-Lbs., enough to be adequate for whitetail-size game, but nothing larger, if you believe the KE proponents). It yielded thorax traversing hits on all shots. Given a reasonable shooting angle it would be fully adequate for trophy class buffalo, and any pig.

A word of caution is in order. As the arrow’s mass diminishes attention to each of the other penetration enhancing factors becomes increasingly more important. On those barely above threshold UFOC arrows you’ll need to get the arrow as well tuned as possible. Both the broadhead’s Mechanical Advantage and the broadhead’s design, sharpness and ability to retain that sharpness become very important factors. These are all major factors in increasing the Transfer Efficiency of whatever force your arrow carries at impact.

Ed

[Kaninmaskwa]

Hi Ed thanks for the reply. ( I heard you were going to be far from a computer for a while )
I will reread part 4 I must have missed the speed part ( I knew I should have been using a highlighter)
Basically I'm trying to determine the minimum bow power I'll need to get the job done, I'm looking  to buy a new efficient hybrid long bows and want to keep it as low poundage as possible.
In fact if the low 160FPS speed is sufficient I will now consider a few extra pounds to get a bit more speed, add more arrow weight or keep  the bow poundage as low as possible.
Decisions..........

[Dr. Ed Ashby]

I decided I had to get a computer connection because there’s not much other communication out here; not even a radio station I can tune in to. Don’t get that much time to go online though. There’s at least a few years of work needed to build this place up, and a lot I’ve got to get done before winter ( and hunting season) sets in.

You didn’t miss the velocity; it’s not there. I rarely mention the velocity of any of the setups but it’s easy to calculate from the Momentum and KE of the setup. If you don’t want to do the calculations yourself there’s a Momentum and KE calculator at  http://www.tuffhead.com/education/formulas_momentum.html.  All you have to do is plug in the arrow mass and try different velocities until you get the matching Momentum and KE.

Your draw length will affect the bow weight you’ll need to reach that velocity too. I shoot with a relaxed, bent arm form, and only draw 27”. When we were playing around with some of the ACS-CX bows at the Abowyer shop, using the same weight arrow, one person with a long draw was able to get the same chronographed velocity from a 49# bow as I was getting from a bow in the low or mid-sixty pound range. (Can’t remember the exact weight if the bow I was using that day without doing a lot of searching through old notes.)

Ed

[Kaninmaskwa]

Thanks again Ed for all your insight. I wish you all the success on your new place.
I'll fool around with the calculator. I'm Drawing 28" and looks like with the right bow I could get away with a 50lb bow.


Cheers
Shawnee

[Mike Vines]

I was looking forward to reading the tuffhead site, but it keeps saying site not found.  Maybe later when I check back it will be available.

[Dr. Ed Ashby]

Try this link. It worked when I just tried it. It takes you to the TuffHead home page. Once there, look on the left margin under “Reference Room” and click on “Kinetic Energy vs. Momentum”. At the botton of that page you’ll find the Momentum and KE calculator.
 http://www.tuffhead.com/broadheads/tuffhead%20main.html.  

Ed

[Kaninmaskwa]

I image there would be a way ( for someone much more intelligent then me) to graph/chart the optimal momentum for each bow.
What I picture is that there will be a certain point where the speed becomes too slow for the weight of the arrow.
Is that the minimum speed for every arrow weight?
For example if you can shoot a 660gr arrow at 170fps is it better to increase the weight of the arrow until it shoots at 164fps,163,162? At what point does it become a trajectory or personal issue?
Another way to look at it if your shooting a 720gr arrow at 158fps is it better to go a bit lighter to increase the speed?
In these examples I'm talking about lighter Bows with arrows that are being set up right around the bone threshold weights. Assume that the arrows are set up for near optimal flight tuning and penetration (I say near to allow for a realistic approach for when things are less then perfect)
Would a pound or 2 really make a big difference?
Inquiring minds want to know...........
I don't mean to be asking so many questions, I see my early calculations and thinking were in the ballpark but I after re reading through the papers I can't seem to figure out how to find that crossover point, that optimal balance of weight vs speed.
Here's hoping my arrows fly faster than my I.Q.

[vintage archer]

Mike, try this link,
 http://tuffhead.com/education/formulas_momentum.html
After posting I will try it from tradgang. Somehow Dr.Ashby is getting extra characters added to the link.
If you do get to the correct site go to bottom of the page for the calculator.
If you get a chance read the comparison of momentum and KE on the same page. When we get maxed out on the weight of bow that we want to shoot the only way to compensate is with a heavier arrow. May be this discussion will help. If you still have doubts post again I am sure Dr Ashby can help us.

[vintage archer]

Mike, the link works it must be the weather in Texas playing havoc with Dr. Ashby’s computer

[pdk25]

Not trying to cause troubles, but I don't thnk that my goal would be to use the minimum that I could for dangerous game. Dr. Ashby has done a lot of great work, but I don't think the numbers include a slight crosswind, or when you glance of some grass blades. Just me. Carry on.

[kuch]

Kanin.  , here's my thoughts: I think I understand what your asking in your last post,but i believe "tuning " for a certain weight/speed is the wrong direction. I think the bone threshold weight is a baseline then tune from there. I have found that there are just some combos of shafts/head weight that fly and tune great out of certain bows and also are above the bone threshold,ie 720g at lets say 155fps. Let's say That setup flys perfect and consistently. Yes ,one could tinker endlessly to try to get higher speed and still stay above the bone threshold weight....but we know that this first  set up flys perfect out of this bow and you have confidence in it. And the bottom line is to kill animals,not have a set up that is "perfect on paper".i am not discounting any of the research done. It is extrememly valuable , but sometimes there's a "magic bullet" that just fires great out of a certain gun,that doesn't necesarily match the "perfect" reccomedation.I feel one should go with it."Another way to look at it if your shooting a 720gr arrow at 158fps is it better to go a bit lighter to increase the speed?" I think if that set up is the " magic bullet" out of that bow ,then no.
Lot's of coffee this am

[Javi]

Every bow will have a sweet spot where the arrow weight/speed is optimized if you really want to fiddle with it you will need a good chronograph and a good selection of arrow weights… You will see a peak where the weight increase/decrease in relation to speed loss/gain falls off rapidly..
Personally I no longer fool with stuff like this.. about the only thing I worry about is using the chronograph to optimize brace height/spine relationships..

[Shawn Leonard]

I love Javi's posts, no nonsense and always make informative! Shawn