Current setup Mathews Z7 28" 65# Shooting 5575GT 100gr tip 376gr total weight. Chronoed at 286fps. Will hopefully be shooting a Fixed blade cut on contact head like VPA or Montec.
I am wanting to get to 400-450 gr range. If I go to a 125gr broadhead, I am marginally spined. If I increase my Draw weight to 70, then I am marginally spined regardless of tip weight. If I go to a 150gr broadhead I need new arrows.
It looks like I am out of luck with my current arrows. How can I evaluate all the factors and get a representative idea of what a 425 or 450 gr arrow will shoot like at 65 and 70#. Above what speed does tunability of broadheads and bow noise become a issue.
Is there a "sweet spot" of speed that within which you get all the advantages without the disadvantages?
I bet if you post the specs of your current and proposed arrow someone will run it on one of those software programs for you to see......
Current configuration Z7 28" 65# 375gr
Proposed Same draw but between 65-70# draw and arrow weight between 425-450gr.
Matt: Any trajectory calculators out there?
The better YOU are at shooting, the smaller the vanes can be, and the less offset/helical you will need, resulting in a flatter trajectory. But only you can answer that for yourself. It's better to error on the safe side I believe.
Definitely go to the next heavier spine arrow, increase the length of the arrow as needed, and increase the point weight. If you have a favorite arrow shaft(or two, or three), I would be glad to give you some setup options.
Yesterday I was shooting indoors at 25yds (60lbs @ 29") 3 arrows with a 125gr TP vs 3 with 150gr TP...the difference between the groups was 1" at the most.
Another example...while shooting indoors at 35yds (arrow weights from 375-440grs) all the arrows grouped within a 2" circle. I did this just to show someone at the range just how minor the difference really was, he too was thinking the difference would be great.
Take into consideration you increase draw weight to 70lbs, a 425gr arrow will will most likely hit within 1" of your 376gr arrow, and I would bet a 450gr arrow won't be that far off. The trajectory of the arrow will carry the same flight out to about 50yds.
My point is don't get caught up thinking your pin gap is going to change drastically, once adjusted, you probably won't notice the difference.
As far as hitting the 9 to 10 inch pie plate... I suppose if that is as accurate as you want to be, so be it... it works. I once read an article written by Randy Ulmer. He said that close is not good enough, he likes to be right on. I have the same opinion. I want to be exact, not "close enough".
One additional question - My current arrow GT 5575 weighs 376 grains. It is 29" long. So 29 * 8.6 = 249.4. Add in a 100gr tip thats 349.4. Insert @ 11.4 and nock at 11.5 brings me to 372.3
That leaves 3.7 grains for the 3 vanes that I have. On the GT Site, they list the 1.5" HP Vanetec vanes at 3.1gr - I thought that would be weight for each vane, not a set of 3. Somewhere I am missing a few grains.
Now to find the combination arrow/tip that will get me to 425-450gr range with a 125 or 150 gr broadhead...
Also what vanes are you using to ensure stabilization: The 1.5" HP Vanetecs or something else?
With the heavier setup my pin gaps were huge, as X-man said I think I have to look into my vanes as I'm shooting 3.5" Quckspins, like them but suspect they have some some serious drag. I used to think it didn't matter with a rangefinder but sometimes I'll range something close to an animal so the yardage may not be perfect, and with less than perfect form a little high or low you could be off that cirlcle a lot faster.
Did you weigh your shafts before you built them? The 8.6 gpi is an "average" that Gold Tip has in that shaft spine size, not an absolute weight.
Speed Calc: http://backcountrybowhunting.com/articles/calc/ Trajectory Calc: http://www.outdoorsden.com/archery/archbal.asp
The speed calculator estimated the same fps that I chronoed with my bow - so it gave me a little bit of a comfort factor with the numbers I was seeing.
So I used the speed calculator to determine approximate speeds for my current setup 375gr arrows at both 65 and 70# draw weight as well as 425gr arrows:
375 @ 65# = 288 @ 70# = 298 425 @ 65# = 273 @ 70# = 283
I then went to the trajectory calulator andtried to factor in 2 exagerated "Missjudged Yardage scenario" What if I used the 20 yard pin at 40 yards and the 30 yard pin at 40 yards. here is the results 20/40 - used the 20 yard pin at 40 yards - inches below aiming point that arrow impacted 30/40 - used the 30 yard pin at 40 yards - inches below aiming point that arrow impacted
20/40 30/40 375 @65# -17.0 -8.9 375 @70# -16.5 -8.3 425 @65# -19.7 -9.9 425 @70# -18.3 -9.2
So what this is showing me, is that adding 50 grains to my arrow will affect my point of impact in the 20/40 scenario by 2.7" and 30/40 by 1" without changing draw weight. If I bump my draw weight up to 70# I will be altering my point of impact by even less - 20/40 = 1.3" and 30/40 = 0.3.
What I was trying to evaluate here was Given the 2 setups 375@65 and 425@70 what would a missjudges range do to my shot - basically nothing.
So just to see what the differences were in the 2 setups to the overall trajectory - I used the trajectory calculator with a 0 yard pin. Below are the 40 yard points of impact
375 @65# -33.8 375 @70# -31.6 425 @65# -37.7 425 @70# -35.1
** For grins I ran 450 @70 and got a drop of 36.9 **
The difference between 375 @65 and 425 @70 are minimal ~ 1.3 inches. Being able to bump the draw weight to 70# appears to have a very positive impact to the equations...
Given the data above 70# GT7595's and a 125gr broadhead shouldn't change things too awful much in the trajectory arena - but should provide a lot of improvement on whatever I hit.
Any Thought? Comments?
The other option to keep your current arrow and not cut them (if you don't have any room left to shorten them) is to drop your poundage to say 60# and go with a heavier tip 125, give you a 400gr arrow but a bigger pin gap.
A couple years ago had a similiar set up- 30" draw 63# bow with GT 5575 cut to 28.5" with 100gr tip for about a 375gr arrow. This worked great on whitetails. It was marginial on spine so when I moved to elk country again I bumped my poundage up to 68# and went with a 340 spine easton st epic nano at 29" and stuck with a 100gr bh since I had a bunch. The arrow goes about 425gr. I have been leaning toward a 125 gr tip to give me a 450gr arrow which may help a bit with elk.
I would get a new stiffer arrow which would inherently put you over the 400gr point. bump your poundage up a couple pounds if you are worried about pin gap, but bottom line accuracy is more important than speed.
Hopefully its a double enter
First Chart 20/40 30/40
375 @65# -17.0 -8.9
375 @70# -16.5 -8.3
425 @65# -19.7 -9.9
425 @70# -18.3 -9.2
40 yard zerod at 0 yards 375 @65# -33.8
375 @70# -31.6
425 @65# -37.7
425 @70# -35.1