Correct arrow weight/spine for my bow?

[SHOT44]

I am a bit confused about arrow spine vs arrow weight for for my hunting arrows.

currently I am shooting a Bear Truth 2 bow at 70 lbs, I am using easton axis fmj .
arrows are 28 inches and they are 340s and 11.3 gpi

are these the right arrows for me?
they shoot really well but i have heard that not enough spine causes the arrows to bend backwards when they hit causing the arrow to not penetrate well

I also have some of the same arrows in 400 and 10.2 gpi but they are 29 inches long

I shoot 100 grain Rage broadheads so that would make my current hunting arrows about 450 grains.

any advice would be really appreciated

[Vader]

What is your draw length? I suspect you might be marginal in the spine area but without seeing what the flight/grouping characterstics are and your draw length I would be guessing.. What is "really well". A 4 inch group at 30 yards? Not trying to be gritty but, what is reasonable or really well to some is insufficient for others. It would help if you can be a little more specific.
It has been said by many that a good hunting arrow should weigh 400 grains and up for best penetration. I myself shoot a 397 grain arrow @ 28.75 inches of shaft for hunting..

[SHOT44]

my draw length is 29, and my arrow groups are around 3 to 4 inches at 30 yards, and my arrows are 450 grains at 28 inches.

[Bowzone_Mikey]

your spine looks alright by me with 340s at 28" throat to tip ....at 70# draw weight

Bear truth 2 bows are pretty good for what they are as are FMJs

I am willing to bet your 400s dont group as well as your 340s

Spine isnt really about how they bend at impact ... its how they bend coming off your bow and how quickly they recover in flight with the weight, agresiveness of your cams, power stroke of the bow .... also with the tip weight will have alot to do with it .... I suspect you could tighten up your groups with the 400s if you shot an 85 grain head .... you could open up your groups with your .340 spines by putting on say a 150 grain head etc....

[SHOT44]

thankx for the insight bozone m im new to bowhunting so im still learnin. am i correct in the assumption that the higher the number ie. .400 the lower the spine?

[Vader]

Shaft spine is on the stiff side of things which is easier to tune and safer than a weak spine. Shooting 125 grs would be closer to spec but if you are happy with the present performance then you are good to go. Weight would be in the 479gr depending on type of fletching if you did 125 gr. These are one tuff shaft but there are others that would reduce weight giving flatter trajectory and still give you pass through performance and reasonable durability.

400 is weaker than 340 in the easton line.

[Bowzone_Mikey]

Spine actually refers to the amount of flew an arrow has .... suspend the arrow at 2 points ... I think its 29" apart ... I cant recall the exact details but for the purposes of this post they are not important .... Now you hang a weight at the mid point ...(again I cant recall the exact weight) the amount the arrow shaft flexes under this weight in thou of inch is the spine of the arrow ... for example if the shaft flexes 1/2 inch then the spine would be 500 or .500

the higher the spine number ie:400 the more flex it will have ... and thus is suitable for a lower poundage /less agressive cam

Now those numers are for Easton arrows as they make the most sense to me ... Carbon Express uses numbers like 5575 series ... what that means (in a nutshell) is that those arrows when cut to 29" and outfitted with a 100 grain point they should be suitable for most bows between 55 pounds and 75 pounds draw at 28"

You can fiddle with spines by trimming the arrow down .. lighter heads .. etc....

for example I am planning on hunting with some 400 spine arrows out of a 70 pound bow .... they weigh a total of 353 grains ... but they are going 322 Feet per second making for 81 foot pound of Kinectic energy ... they are trimmed as much as they can be and fly fantastic .... and perfectly legal for everything but Bison (which is bullsh*T..but thats for another thread... Bison requirements are 50 pound pull and 400 grain arrows... I know of a 50 pound bow that can shoot a 400 grain arrow 243 FPS and it only generates about 52 pounds of KE)

its all good SHOT

[Bow Walker]

Been away for a couple of days - moving, but now I'm back.

BZM has given you the correct "poop" on your question, SHOT.......shoot with confidence.

[knockturnal]

your setup is identicle to mine. 70lb bow, FMJ arrows are cut to 28", 100gr broadhead, fletches and nock, all adds up to 440gr. The bow shoots 295fps. Who cares about spine. Pick an arrow weight. for me, it was 440gr. Minus the broadhead, inserts, nock and fletches and you are left with the bare shaft. 28inches of the 340 spine FMJ gets me to my 440gr.

PS They group great.

[Bowzone_Mikey]

your setup is identicle to mine. 70lb bow, FMJ arrows are cut to 28", 100gr broadhead, fletches and nock, all adds up to 440gr. The bow shoots 295fps. Who cares about spine. Pick an arrow weight. for me, it was 440gr. Minus the broadhead, inserts, nock and fletches and you are left with the bare shaft. 28inches of the 340 spine FMJ gets me to my 440gr.

PS They group great.

what inserts knock and flecthes do you run that are only 24grains combined ... 28 x 11.3(grains per inch) = 316 (ish) add your 100 g BH that brings you to 416 leaving you with 24 grains to get 440 ... since your average insert is about 13 grains ... blazers are about 5 each ... a nock is about 13 as well ....

Just saying ... I suspect your closer to 460 with your setup than 440 ... not that it matters much

[knockturnal]

I'm pretty sure it's 440. I could have had a brainfart and it's 460. I'll measure again. Either way, it's still a heavy arrow at 295fps

[knockturnal]

My bad. I shoot 400s

[Bowzone_Mikey]

My bad. I shoot 400s


Its all good ... I was hoping you shot 340s and found some super light compoents somewhere ......;)