I've taken some grief on my opinions about arrow weight, so maybe I can clarify my views a bit.

I view momentum and KE both as parts of the same puzzle though, in my view, momentum is the key. For a given bow, both KE and momentum increase as arrow weight increases. However at a certain point, arrow weight will get too heavy for the bow. KE and momentum don't increase as much and trajectory goes completely down the tubes. The arrow has gotten out of the bow's efficiency range.

Try as they might to change things, arrow weight selection is still a matter of tradeoffs and balances. You can't have one thing without giving up something else. To get best speed and flattest trajectory, you sacrifice KE and momentum. To get highest KE and momentum, you must sacrifice speed and trajectory.

Lets say a bow's safety and efficiency ranges run from 5 grains per pound of draw weight to 12 grains per pound. Then you can draw a line chart like this:

Light ----------------------------------Heavy

Trajectory ---------------------------- KE & Momentum

5 gpp-----------------------------------12 gpp

_________________^__________________

On my compound, I like my arrow weight to be from the middle to about 3/4 way up the heavy side, about 8.5 to 10 gpp. I shoot a 60 pound, round wheel bow at 33.5" draw. With my stickbows, I want that arrow weight up around 10-11 gpp. I have a long power stroke, 25" or so, and heavier weights are more efficient. (Think of a golf ball and a pingpong ball. Use a long, hard overhand throw and the golfball goes a long way. The pingpong ball just kinda flings out there a few feet and falls to the ground.) Also, I don't produce extraordinary amounts of KE, so I compensate for that by having increased momentum.

If I was shooting heavier poundage and hard cams, I'd probably slide my selector a bit to the light end, around 7-8 gpp, and still have plenty of oomph for hunting anything in North America.

For someone with a shorter power stroke and heavy enough draw weight, to still produce gobs of KE, they can slide the selector button over to the light side, say 6-7 gpp. (Using the golfball/pingpong ball analogy again, thump the pingpong ball with your finger and it rockets across the room. Thump the golfball, and it just rolls across the table while you grab your bruised finger and howl.[:-]) The lighter arrow is more efficient with the shorter power stroke.

Now, for someone that does not shoot a heavy draw and has a short draw length, they tend to slide the selector button even further to the light side, to get better trajectory. This is fine for a 3D arrow, but a big mistake for a hunting arrow. In order for them to get a deep penetrating hunting arrow, they need to slide the selector button UP the weight scale. They need to do like I do and compensate for their low KE values by maximizing their momentum. The less KE they produce, the further up the scale they should go. Of course, they will make some sacrifices in trajectory but with a low KE setup, they don't have much business taking hunting shots beyond 25 yards anyway. IMO, people would do well to maintain their minimum arrow weight at no less than 400 grains. Weights lower than that should be left to highly experienced people that know EXACTLY what they are doing, and are prepared to deal with the risks they know they are taking.

Then broadhead selection becomes part of the issue. When going less than 40 ft lbs of energy, I'd shoot nothing but cut on contact type heads. I would not shoot mechanicals unless I had 60 ft lbs or better. I'd want even more KE with the wide cutting, multiple blade mechs.

Great post!!! And it is exactly what experience shows us. I think that the newer bows are tightening that range up a bit, but the reasoning there still applies.

I totally agree. I have been shooting arrows in the 9 gpi area for quite a while and get total pass throughs, even on a doe I hit slightly forward and in the leg. It broke the left front leg and was sticking in blowdown on the other side. This at 26 yards.

Years ago, I was shooting 2117 SS aluminums out of an old 1988 Golden Eagle softcam bow and still passed through at 30 yards.

I do have to say that in recent years, arrow weight is becoming somewhat less of a factor as the bows are getting more efficient and faster. I'm not saying you don't have to stay in a reasonable weight. But I think with todays typical bowhunting setups of 60-70lbs, 28-30 draws, you can get more than enough KE out of a 6-10gpi arrow.

Why do you think some states have a 400grain minimum arrow weight? More ooomph, especially for larger game like bear and elk.

Here is a question I have. Most of us know how important a correctly spined arrow is to efficiency and tuning. A lot of energy is wasted in an arrow during its recovery stage during the shot. Meaning the flexing of it. I know that an arrow that is too stiff is not "correctly spined". But wouldn't it recover much faster and keep more of its inherited energy from the bow?

Great post!

I have a question. What is the difference between Grains per pound (like your measuring it) and grains per inch (like muzzyman measures)

Grains per inch seems easy enough to figure out but I'm confused on the Grains per pound. I do know that there is a difference. Can someone explain?

Thanks!

Grains per pound is finished arrow weight. It is calculated by taking the overall finished arrow weight, divided by the draw weight. ex. 500 grain arrow at 70 lbs. 500/70 = 7.14 grains per lb.

Grains per inch is the unfinished arrow weight.. ie- the bare shaft. ex - 9 grains per inch shaft x 30" shaft = 270 grain shaft..keep in mind however, that this is without insert, tip, nock, and fletchings.

Also, Arthur, excellent post. Probably the most thought out and best illustrated post I've seen here in a few years. I tend to agree with you. When hunting, the added momentum of a heavier arrow, more than makes up for the loss of trajectory. Especially with rangefinders.

Arthur,

Not to sound younger than I am but....

Dude, You Rock!

That was an excellent post. You are getting a HRAOP for that one! Very well put and some excellent examples.