Arrow build question: 340 spine or 300 spine?

[cpalm9]

I'm glad you ended up cutting them at 27" rather than 28". That increases the dynamic spine and should broadhead tune really well. Like I said previously I would always error on the stiff side with broadheads! Good shooting!

NC

Sent from my SM-G970U using Tapatalk

Yeah I’m happy with the length as well. I plan to use either slick trick viper tricks or QAD exodus full blade, both in 100 grain. I suspect there won’t be much tuning necessary

 

[Red Letters]

Does 27” mean carbon to carbon or did you include the nock like the nock on chart?

 

[Latebloomer]

I would do 340's if it were me, 300's will be on the stiff side and like you mentioned heavier. I'm shooting 73lbs, 28" Draw with 300's and have 100gr inserts, 25gr collars and 100gr heads, I also have lightweight fletchings. I agree with the above about using a shorter arrow. I'm shooting a 26.25" arrow with an inch long collar at 28" draw.

What’s your arrow weight and velocity?

 

[nphunter]

What’s your arrow weight and velocity?

500gr right on the money, only because I'm lazy and don't want to have to resight my bow when I change arrows. My sight hasn't been adjusted in years, I shoot right at 280fps. When I get a new sight I will most likely drop back down to around 450gr. I have always hunted OR and ID which didn't allow expandable heads until recently, ID 2020, this was the reason I liked 280fps.

 

[Latebloomer]

500gr right on the money, only because I'm lazy and don't want to have to resight my bow when I change arrows. My sight hasn't been adjusted in years, I shoot right at 280fps. When I get a new sight I will most likely drop back down to around 450gr. I have always hunted OR and ID which didn't allow expandable heads until recently, ID 2020, this was the reason I liked 280fps.

I guess the new phase 4 bows are slow. Drawing 70lbs with 509.5 grains and only getting 262 fps

 

[Mighty Mouse]

I guess the new phase 4 bows are slow. Drawing 70lbs with 509.5 grains and only getting 262 fps

What's your draw length? 509.5 gr at 262 fps is about what I would expect at 27.5-28" DL.

 

[nphunter]

I guess the new phase 4 bows are slow. Drawing 70lbs with 509.5 grains and only getting 262 fps

I shoot an RX4 with a #2 cam set at 28" and the draw weight is 73lbs. It's shooting 278fps and my arrows weigh exactly 500gr. That is one of the main reasons I've always shot a Hoyt with #2 cams, they were always most efficient at 28" where most bows are shooting off the lower end of the efficiency at that length.

 

[Latebloomer]

What's your draw length? 509.5 gr at 262 fps is about what I would expect at 27.5-28" DL.

28, but I’m seeing others with another 20fps roughy

 

[Mighty Mouse]

28, but I’m seeing others with another 20fps roughy

Have you measured your draw weight? Having 70# mods with limb bolts fully tightened doesn't guarantee 70# draw weight. Your bow could be drawing a bit light and need some cable twists.

Phase4 29 advertised IBO speed is 340 fps (with a 350 gr arrow). Using 10 fps per inch of draw length rule of thumb would predict a 350 gr arrow flying at 320 fps (79.6 ft-lbs KE) at 28" DL. Holding KE constant and solving for speed with a 509.5 gr arrow predicts 265 fps. That speed estimation method ignores some nuances (effect of weight on string, effect of arrow weight on energy efficiency) but is usually accurate to ±5 fps. Higher let-off mods (85% instead of 80%) would shave off a little speed. If you happen to be shooting the 33" ATA model, you're starting off 4 fps slower than what I estimated.

 

[Latebloomer]

Have you measured your draw weight? Having 70# mods with limb bolts fully tightened doesn't guarantee 70# draw weight. Your bow could be drawing a bit light and need some cable twists.

Phase4 29 advertised IBO speed is 340 fps (with a 350 gr arrow). Using 10 fps per inch of draw length rule of thumb would predict a 350 gr arrow flying at 320 fps (79.6 ft-lbs KE) at 28" DL. Holding KE constant and solving for speed with a 509.5 gr arrow predicts 265 fps. That speed estimation method ignores some nuances (effect of weight on string, effect of arrow weight on energy efficiency) but is usually accurate to ±5 fps. Higher let-off mods (85% instead of 80%) would shave off a little speed. If you happen to be shooting the 33" ATA model, you're starting off 4 fps slower than what I estimated.

Good information. I actually didn’t measure my draw weight when I bought the bow a couple weeks ago. Only 3fps off from your estimate and I’m at 85% let off.

 

[Prestjd]

I'm setting up some new arrows for elk this season. Planning on using Easton Axis 5mm. My draw length is 27.5" so I think I'll do 28" arrows as that is what seems to fit best with how my rest is setup. Last time I checked, the shop said my draw weight was around 67lbs.

I want to build an arrow that's around 450 grains. My question is because I am adding more to the front of the arrow such as a 100 grain broadhead and the 75 grain insert, would I be better off on a 300 spine vs a 340 spine? Easton recommends both spines so I'm just not sure which would be ideal. A 300 spine would get me closer to 475 while the 340 spine would be more around 450

I'm shooting 27.5" draw and 65#,340 spine axis match 5mm, 75 grain insert. 4in wrap, 4 fletch match hunter vanes , with 100grain head with out issue. My arrows are 28.75"

 

[Elkhntr08]

I’m shooting 5mm Axis and FMJ 340s pretty much out of all my bows. Have some 300 FMJ for elk and moose. Ordered some Axis 300 to play with. Shooting 70# with a 27 5/8” shaft. Run a VAP footer on everything and wraps.
Tuning the arrows have never been a problem.
I’d rather be on the heavy side of the spine chart the low side.

 

[jbond007m3]

the math puts you at 340 all day. So unless you plan to get your point weight/FOC much more.... then 340 is nice.