Isn't a 650 grain arrow a "650 grain arrow"?

[Richie Nell]

Maybe you who know more (everyone) can help me understand the following philosophy:
So many people go with the philosophy of 10 lbs. per lb. of bow weight to be OK with their arrow setup.
What difference does it make about the bow weight.  If the weight of the arrow is so important, which it certainly is, why decrease the arrow weight requirement as the bow weight decreases.
For example, if arrow's "bone busting threshhold" or the standard recommendation is 650 grains then it is "650 grains".
At the same time, in the same breath, why would a 50 lb bow shooting 10 gr. per lb. of draw weight (500 grains) be the recommended thing to do. Or a 45 lb bow shooting 450 grain arrows, etc.
This seems to me to be contradictory.  Either a specific grain arrow is the more correct recommendation or it isn't.
A specific grain arrow per lb. of draw weight just doesn't make any sense.  That philosphy  simply puts all bows with the corresponding 10 grain/lb. draw weight on the same playing field.  And that is certainly not true.  

Any explanation is welcome

Richie

[Bowferd]

I believe that all charts and recommendations must begin somewhere. From studies thru trial and error what we have here is a starting point.
 There are exceptions to every rule but the bottom line is that we have a starting point. And to the curious, now the fun begins!

[Cootling]

Richie,

The 9-10 grains/pound recommendation is intended to achieve a balance of acceptable trajectory, shooting qualities, and impact energy.

Glen

[laddy]

The difficulty in this hypothesis comes when you have a bow with not exceptional cast that likes heavy arrows, like an osage cored longbow versus a bamboo cored bow of the same design.  The slower bow even though it would not be as affected by arrow weight does not have the cast to shoot a stiffer arrow.  Then your choices get into slower recovering hard woods and suddenly a whole raft of variables come into play.  Trial and error fun times.

[30coupe]

As laddy mentioned, each bow handles arrow weights differently. The 10 grains per pound of draw weight will get you close.

Here is an analogy for you:

A mean little kid stands at the street with a bucket full of rocks of various weights. With an evil gleam in his eye, he picks a large rock from the bucket and chucks it at your picture window. It is too heavy for him, so the rock falls on the lawn far short of the window. Undeterred, he picks the smallest rock from the bucket and fires away at the window. The rock hits its target but isn't heavy enough to break the thick glass. Finally the persistent little turd pulls a medium sized rock from the bucket, aims for the upper half of the window and puts the rock right through the middle. After pausing briefly to survey his work, the little peckerhead beats a hasty retreat.        

Okay, that was a long analogy, but the point is the total weight of the arrow needs to match the cast (not just the draw weight) of the bow. Like the nasty neighbor kid, you will have to experiment a bit to find the best combination, but 10 grains per pound of draw weight is a good place to start.

[Molson]

The mean little kid should have snuck closer to the window, threw the heavy rock, and broke, not only the window, but the coffee table on the other side too!!   :eek:      :D

[Richie Nell]

30...I do understand your point. That has to do with getting a matching arrow based on deceent trajectory, not too heavy, not too light for shooting purposes.  It has nothing to do with what it takes to penetrate an animals body. And that is what the intentions are when the bone busting threshhold is recommended to be 650 grains.

It seems like the recommendation or standard to go by should read something like this:

The bone busting threshhold should be a 650 grain arrow traveling at a minimum of 140 fps.

TO ME  that makes more sense because it doesn't matter what the bow weight is....you just need to get THAT arrow going THAT fast to get the job done..period.

[laddy]

However, a strong shot out of lighter weight bow even with a shorter draw and lighter arrow can out penetrate the slower flying heavy arrow if it is not flying clean.

[30coupe]

Richie,

It depends on the job at hand. If you are hunting whitetails (the most common big game animal in North America) 650 grains is more than sufficient. If you are after Cape Buffalo a 650 grain arrow is minimal (personally, I'd prefer a 500 grain solid at about 2500 fps   :D ).

I try to shoot them where the bones aren't. Still, arrow weight is only part of the equation. The broadhead is also critical. Ashby also says the shaft material is critical to penetrating heavy bone (he prefers wood).

Good topic anyway!

Molson  :p  

 

[Richie Nell]

oh yea I fully understand all the other factors that go into getting good penetration.  Not my point.

For example a common question that comes up is:
"What arrow weight should I use with my 50 lb. bow to hunt elk?"

I have seen answers that suggest 10ish grains per lb. of draw. (500 gr.)

And other answers something like...."you need at least a 650 gr. arrow for elk."

Again...the bow weight is irrelevant if the bow can send the proper weight arrow at the proper speed.....not because it is a certain grain per lb of draw.  
Draw weight is irrelevant.  It just so happens that most low draw weight bows can't get the job done.

oh well...that grain weight per draw weight is just irrelevant to me (other than the Black Widow warranty)

BTW...I shoot about 11.5 grains per lb. of draw.

[LKH]

Richie, you want a double.  That way you can shoot a 400 grain arrow for trajectory and when it arrives it can be 700 grains.  

You have to pick a balance for how and where you hunt.  I am willing to give up some weight to get a little better trajectory out to 30 yards since I do a lot of open country.  Still, I want at least 550 grains out of my 63# bow.  With a good two blade and if I avoid the shoulder, I get enough penetration and still avoid the fat rock trajectory.

[Bjorn]

I have wondered about the same thing Richie.......in my mind a 600 grain arrow out of a 50# bow is better than a 500 grain arrow any day when it comes to penetration.
Trajectory means nothing unless you are using a reference sighting method, and those are fine too-use what works for you.
And even then, trajectory is pretty much non-existant at 15-20 yards with a decent equipment choice.
I think Fred and the gang were looking for a 'marketing simplification' when they came up with 10 GPP.

[Mr.Chuck]

I think 9-10 grains per pound is about right. That gives me the most proficency from the bow without sacrficing speed or trajectory.  Some bowyer recommend this for their bows, on the average.  It works for me. :-)

[Stringwacker]

I think the 9/10 grains rule is about maximizing the performance of a given weight bow. A 500 grain arrow out of a 50 pound bow is probably the best match of speed, balance and penetration. Yet that being said, it's till only a 50 pound bow and that's fairly marginal for elk for example. Certainly, if one was only expecting a 15 yard shoot, it would be perfectly fine to shoot the 650 grain arrow out of the 50 pounder. As many have said, your talking about a rule of thumb and not a specific case by case example of what works best.

[JOKER]

As we learn more about arrow penetratoion through experments such as Dr Ashbys we learn more and more that in order to get the total picture of arrow performance you have to look at all the aspects not just one or two. AS was said before a statement like "10gr per pound" is only ment to get you in the ball park of trajectory and penetration. You cannot compare a 30lb bow 300gr arrow with a 70lb bow 700gr arrow in penetration.

In the same respect you can't just say a 650gr arrow will always work. Try shooting that from a 30lb bow. Dr Ashby was just saying that 650gr was the min threshold to break heavy bone.

Even if you make a statement like 650gr arrow going 150fps is enough to ... You are still leaveing a lot of info out, what point, what arrow how much FOC.... AS Asby has observed if a point or arrow fails (bends or breaks) your 650gr arrow at 150fps will still not be enough.

Just remember general statements are just that. They give you an idea of what is going on but not the whole story.

[Rico]

The 10 grain per # of bow weight is for bow effinceny you have to choose the correct arrow weight/speed a 40 lb bow is not going to shoot a 650 as fast or as efficent as a 65

[Rob DiStefano]

I'm not all that sure what this topic is about but ... aside from broadhead efficiency and arrow spine/flight, I wanna use as heavy an arrow as possible at as fast a speed as possible for medium/large game.  

"Heavy but fast" - that's an oxymoron that begs compromise, and each of us needs to figure out that equation for a given bow's draw holding weight.  

Most bows are happiest when mated with heavy arrows, and I won't go below  10gpp for a deer/hog hunting arra.  Lighter than 9gpp and the bow limbs and riser may have a problem absorbing the excess energy that won't transfer to the arrow, and yer bow hand will know that real quick.
 
YMMV.

[wingnut]

I like about 11 gpp and have shot standard FOC until reading Dr. Ashby's report.  Now I have ultra high FOC arrows on the brain.  Gotta figure out how to maintain my 11 gpp and get the 25% FOC.  But that's what summer is for.  I will be a lot more comfortable with my 54# bow for elk with this arrow.

Now to get me to go to a 2 blade single bevel instead of my WW.  That will be a different story.

So when you go 650 gr. remember it's not just weight, but balance and arrow flight also.

Mike

[Rob DiStefano]

I'm about the same, Mike - 11gpp and 24% FOC, 29" carbons out of 55# holding weight, WW or Snuffers.  

I'm using a 4x4 high back burned fletch but I like what JC's using and will experiment with a low profile 4x4 burn.

[Diamond Paul]

I think you are worrying about a problem that doesn't exist.  Unless you are hunting elk, moose, or African animals, a well-matched arrow with sharp head is going to give you plenty of penetration.  9-10 grains per pound is going to be a good match out of most bows.  If you wanted to hunt elk with low poundage, then you might need to load up a heavy arrow and accept very short shot limitations, in order to get enough penetration.  But for general use, a 650 grain arrow out of average bows (45-50lbs) is akin to trying to pull a trailer full of wrought iron with a Nissan Sentra.