Arrow Spine Question

[jrebel]

I shoot a Mathews Heli m 70lb bow at 30 inch draw.  My arrows are 29.5 inches long and I shoot 125 grain points.  I shot Easton Axis n-fused 340's.  My last bow was only 60 lbs (everything else being the same) and it loved the 340's.  As I look at the shaft selector on easton's web sight it is unclear as to what spine to shoot, either the 340 or 300.  Is it better to be overspined or underspined??? 

What would you shoot out of this bow?  300 or 340, 100 or 125 grain point. 

Thanks

Johnny

[Button Nubbs]

70lbs, fast bow, long draw, long arrows, heavy broadhead screams .300 to me those charts on the websites dont take into account the speed of a bow which has a MAJOR effect on spine. your best bet is to ask if someone has a spine selection program and see if they will run your numbers. i had archers advantage but the computer it was on went buh bye.

[jrebel]

That would be awsome if someone had a program and could run the numbers.  If it helps I chrono the bow with both 125 and 100 grain points, this was what it chrono's at with my set up.

125 grain point = 293 fps
100 grain point = 301 fps

[JLS]

Wow, that thing is smoking!

[Johnb317]

From a safety standpoint wouldn't it be better to be over spined.    Btw don't forget to figure in foc. 

[jrebel]

FOC with the 340 spine 125 grain point and 29.5 was good.  If I go to 300 spine I will have to do the math again to see if 125 grain or 100 grain is better. 

[washelkhunter]

the Spine measurement was important when shooting the wood bows. im not sure it really applies to straight on mechanicals. When shooting long or recurves spine referred to the stiffness of the arrow shaft. this was important because the arrow once fired had to bend around the riser. this produced a lateral flexion in the shaft of the arrow as it was passing the riser. the higher the draw weight the higher the spine (stiffness) of the arrow needed to be so that it would snap back to true more rapidly while in flight after release.

[RadSav]

70lbs, fast bow, long draw, long arrows, heavy broadhead screams .300 to me those charts on the websites dont take into account the speed of a bow which has a MAJOR effect on spine. your best bet is to ask if someone has a spine selection program and see if they will run your numbers. i had archers advantage but the computer it was on went buh bye.

X2!!!  http://www.archersadvantage.com  download for less than $40.00.  It has to be the best bargain in archery for sure.  You will never regret the purchase.

Sounds like you are a gorilla at 30"!  That does make for a long flat spot at the top of your force draw curve.  Add that to a fast and often fickle little bow and you will want a dang stiff arrow.  I'd be willing to bet even a .300 is going to be weak at 29.5"/70#.

Download the software and you can play with all sorts of configurations to find the best match.  It will also give you a list of all manufacturers arrows that will match correctly.

[coachcw]

with 340's I'd shoot 100 grain broadheads . the heavier the broadhead the stiffer the spine you need .

[RadSav]

Even with a 100 grain broadhead that bow at 30" and 29.5" arrow you'd have to drop weight to about 62# to shoot the 340 spine well.  The 25 grain drop will only buy you about 2 pounds of additional draw weight.

[lokidog]

You should go with the .300's  My setup with the Bowtech Invasion is almost identical to yours (29" draw, 29" arrows, 64lbs) and the calculations showed I was closer to 300 than 340.  I shoot a 100 gr broadhead.  With a 125 I would be right at the 300.

My old bow at 65-70 lbs, same draw and arrow liked the 340's well enough but the new one needed stiffer arrows.

[jrebel]

I am going to buy some 300's and see how they shoot.  The 340's hold tight groups at 20 yards (under 2 inch) at 30 yards it moves to a 4-6 inch group.  Weird thing is it cut's paper clean with the 340's.  I have shot bows my whole life so to hold 4-6 inch groups at 30 yards is not acceptable. 

[RadSav]

Shooting thru paper might get a guy in the ball park, but I find it unreliable.  At other times it can make a guy with a dang good shooting bow abandon everything that's right.  It's sort of like a chronograph...best used to get happy archers to buy something new.

Glad to see you are going to purchase a few 300's to see how they work out. Sometimes you have to test drive a Chevy to see if your Ford is up to par.

There are a lot of pro shops out there that will sell you two or three arrows at a time.  That's plenty to test without breaking the bank.  With your set up I think it will be a winner.  Sure wish Carbon Express would start offering a larger selection of 300 spined shafts.  Most of these new bows I'm playing with really perform better with the stiffer spine. 

Stick with the 125 grain point on those long arrows.  The Axis insert is pretty light so FOC will be much more on track at 125.  If you go to a large heavy vane you might even want to go brass for the insert.  Again Archers-Advantage will really help in trouble shooting a lot of that.  It is not without flaws, but it is far more reliable than the average bow technician.

Good luck.  Let us know what you think of those 300's once you've had a chance to throw 100 or so down range. 

[jechicdr]

On Target by Pinwheel Software is good too.  You can download a trial version and get all the information you need for your arrow spine and optimal broadhead weights.  After I played with the trial versions, I eventually bought the program.  It has some nice simulations that will allow you to play with intermediate distances (between the pins, close distances) and kind of practice shooting off the range, with some wind, at different angles.  I'll tell you your set up is similar to my Z7 and the .300 with a 125 (or better yet a 150) grain broadhead will get you the optimal spine and FOC.  I am thinking of bumping up to 4 vanes though.  At those speeds, those large broadheads can catch the wind and amplify any error in your form or tuning.  I use Beman MFX arrows with 125 grain Muzzy Phantoms (now they make a 150 that I may switch to), and 3 helical blazers.  Invested in a back tension release and laser tuner this year.  Also use Quiktune Sizzor rest from NAP.  Anchor sight from ArcheryInnovations so don't have to worry about my peep.