XT/Outback, Arrow/Pointweight, Speed/KE comparison

[Buckfever]

Outback:
Gt 7595
85grnpoint 381grains 280.5ft/sec 66.58ft/lbs
100grnpoint 398grains 275ft/sec 66.85ft/lbs
125grnpoint 423grains 268ft/sec 67.48ft/lbs
ACC 3-71
85grnpoint 401grains 274ft/sec 66.87ft/lbs
100grnpoint 418grains 270ft/sec 67.68ft/lbs
125grnpoint 443grains 263ft/sec 68.06ft/lbs

XT
Gt 7595
85grnpoint 381grains 285.5ft/sec 68.98ft/lbs
100grnpoint 398grains 280ft/sec 69.3ft/lbs
125grnpoint 423grains 271.5ft/sec 69.25ft/lbs
ACC 3-71
85grnpoint 401grains 278.5ft/sec 69.08ft/lbs
100grnpoint 418grains 274ft/sec 69.7ft/lbs
125grnpoint 443grains 266ft/sec 69.62ft/lbs

The Outback is set at 70lbs with a 28.5" draw, the XT is at 71.5 lbs with a 28.5" draw.
A couple of observations. The Outback sure does seem to like a heavier arrow, with the best performance out of the ACC3-71 and a 125 grain point, but KE goes up appreciably for both the 7595s and the 3-71s with the addition of point weight.

Not as much the case with the XT. It seems to like more spine, with that sweet spot of 417 grains of the ACC 3-71 and the 100 grain point, providing the optimal performance.

I obtained a substantial # of readings so that I felt confident that I was within .5ft/sec.

I thought the results were interesting.

[Twanger]

That is interesting...
Over the range of weights you've tested, the change in K.E. doesn't seem all that significant... only a couple of ft-lb. Also, the speed penalty doesn't seem all that much for he heavier arrows. I.E. just how much increase in 'point blank' range do you get when going from 265 to 280 fps? I'm guessing that it's a yard, maybe 2.

Seems to argue to go on the heavier side for deer hunting.

I just moved up to 410gr arrows, and though I didn't do as detailed a trade-off as you did, the reasoning is supported by your data.

[Buckfever]

I think that at some point I need to calculate the differences in Momentum and add that to the mix in terms of trying to get a handle on what provides the most potential for penetration.

[eshoremd]

buckfever said:

I think that at some point I need to calculate the differences in Momentum and add that to the mix in terms of trying to get a handle on what provides the most potential for penetration.

exactly what i was thinking! i was sitting here wondering when you were going to calculate the differences in momentum and add that to the mix in terms of trying to get a handle on what provides the most potential for penetration. you really need to do this to provide us with a real "feel" for the two bows.

[Buckfever]

"you really need to do this to provide us with a real "feel" for the two bows. "
:-)

Before I do, let me just say that on 2 of the 6 deer that I took with the Outback this past season I did not get complete pass throughs, on those 2 the arrows were hanging by the fletchings. This suggests to me that I am on the border in terms of power for the 2.5" of cut that I used this past season. I think there's too many guys out there pushing big cuts who then blame the broadhead for the wounded animal, spouting things like "mechanicals suck"...blah, blah, blah. There are mechanicals as well as fixed head design out there that suck to be sure. I guess I feel that if an archer is going to move away from the tried and true, they have a responsibiity to the game they hunt to undertand, what is an appropriate broadhead/arrow combination for their setup.

Based on what I experienced this season, 2.5" of total cut require a minimum KE of 66-67ft and .48 momentum. I suspect on a heavy bone hit on a big animal a heavier arrow with momentum up near .5 will get me through. That is the underlying point I'm trying to explore with this.

I'm going through this process principlly to find that optimal balance, between adequate punch and the flatest trajectory that I can maintain while doing so.

[Buckfever]

A couple of guys looked at my data and suggested that the deviation that I observed and my conclusion regarding spine was flawed.

So after rudely I disagreed with them I decided to test it to prove them wrong.

I took the 423 grain 7595 Goldtip and I took the ACC arrow in question, replaced the point with a 103 grain point and a 2grain washer and it came in at 423 grains.

Results were as follows:
Goldtip ACC
272 270
272 272
272 272
271 272
271 271
271 272

I repeated the test again and achieved the same results and stopped the test. If there is a difference between the arrows it is too small to capture with my equipment and it certainly would not be statistically significant. And even if I had the proper equipment and an adequate sample size it's not going to be a big enough difference to matter. At least not to me.

Using the curve fit data provided by Symo at Mathews, the Outback loses 1ft/sec for every 3.669 grains and the XT loses 1ft/sec for every 3.17 grains. I think that sample size is probably large enough so that the differences are statistically significant, don't ask me to calculate that, I'm not that enthusiastic and the curve fit data is certainly close enough.

So for at least .34 spine deflection or less the only factor is total arrow weight.

[Buckfever]

But wait it gets even better.

So I took a Goldtip 5575 which I can not tune even with an 85 grain point. I added a washer and a 100 grain field point and brought that up to 383 grains. I took the same 7595 from before and replaced the 83 grain point with an 85 grain point and got that to 383 as well. Here are the results:

7595 5575
(.34) (.40) Spine deflection

285 284
284 283
284 284
284 284
285 283
285 284
285 284
285 283
284 284
284 284

This is a very exciting result for me. The results are certainly not statistically significant given the low sample size, but I feel that there is probably a very, very small difference. But that is not so much what is interesting to me. What is interesting is that I expected there to be a substanital difference. The issue is that I know that the 5575 is not flying as cleanly, so I can not attribute the difference to spine. Maybe the small difference is a spine issue/maybe it's not. But in any event, even in a case where the tuning suggests that the arrow is underspined, the difference in KE, is so slight as to really not be a factor in spine selection.

Which isn't to say that we don't still desire adequate spine, because we certainly want good flight.

But this result has been very eye opening for me.

[eshoremd]

i would strongly suggest the use of an inverted microbacterial spineometer.

just kiddin, you lost me like two month ago. i still read'em though. remminds me a lot of french class.

[Buckfever]

Basically spine contibutes little to increased KE except for perhaps the case where the arrow is severly underspined. Increasing arrow weight is what increases KE.

Hang on though we have to cover the effect of FOC on penetration yet.