Getting the most from your bowhunting setup

Bowhunting experiences, the best way to tune a bow -- share your knowledge here!
retch sweeny

Posts: 565
Joined: Mon Feb 23, 2009 11:05 am

Getting the most from your bowhunting setup

I’m an admitted bowhunting tinkerer. I’m always looking to learn more. I will start by saying this not a speed thing. Speed is easy to figure. Less weight equals more speed but I’m thinking in terms of a bowhunting setup rather than a 3D, target setup. By more I mean efficiency from the bow and increased penetration. I talking in terms of the Kinetic Energy (KE) and Momentum (MO) outputs compared to draw weight and arrow weight so I started messing around with my arrow weight. For this test I used an older Bowtech (2006 Justice) set at 64 pounds. I used a variety of tip weights and arrow tubes and weight washers to hit the grain weights exactly. I used a “Chrony” brand Chronograph. I started with an IBO arrow weight of 5 grains of total arrow weight (all components) per pound of bow draw weight. This is the arrow weight that advertised speeds are derived from. I then experimented with increasing arrow weights. The following results were achieved.

Arrow wgt: 5 grains per pound of draw x 64 Lbs = 320 grain arrow.

Arrow speed (5 shot average): 277.5 FPS

KE: 54.5 ft/lbs

MO: .393

Efficiency factor (KE divided by draw wgt): 54.5 divided by 64 = .843

Next I tried 6 grains per pound

Arrow wgt. 6 grains per pound of draw x 64 = 384 grain arrow.

Arrow speed: 256.1 FPS

KE: 55.9 ft/lbs

MO: .436

Efficiency factor (KE divided by draw wgt.): 55.9 divided by 64 = .874

Next I tried 7 grains per pound of draw

Arrow wgt. 7 grains per pound of draw x 64 lbs = 420 grain arrow.

Arrow speed: 238.3 FPS

KE: 56.4 ft/lbs

MO: .473

Efficiency factor (KE divided by draw wgt.): 56.4 divided by 64 = .883

Next I tried 8 grains per pound of draw

Arrow wgt. 8 grains per pound of draw x 64 lbs = 512 grain arrow.

Arrow speed: 226 FPS

KE: 58 ft/lbs

MO: .513

Efficiency factor (KE divided by draw wgt.): 58 divided by 64 = .908

Next I tried 9 grains per pound of draw

Arrow wgt. 9 grains per pound of draw x 64 lbs = 576 grain arrow.

Arrow speed: 214 FPS

KE: 58.5 ft/lbs

MO: .547

Efficiency factor (KE divided by draw wgt.): 58.5 divided by 64 = .915

Next I tried 10 grains per pound of draw

Arrow wgt. 10 grains per pound of draw x 64 lbs = 640 grain arrow.

Arrow speed: 203 FPS

KE: 58.5 ft/lbs

MO: .576

Efficiency factor (KE divided by draw wgt.): 58.5 divided by 64 = .915

Next I tried 11 grains per pound of draw

Arrow wgt. 11 x 64 = 704 grain arrow.

Arrow speed: 190 FPS

KE: 56.4 ft/lbs

MO: .593

Efficiency factor (KE divided by draw wgt.): 56.4 divided by 64 = .881

Seeing I crossed the point of diminishing returns in efficiency and KE, I didn’t go any farther.

At the bottom of this you will find a graphical representation of the above data.

Allow me to ponder. Back in 1985 I bought a compound bow and used it for 21 years before buying the BowTech mentioned above. That old bow set at 70 pounds and shot a heavy aluminum arrow with a 145 grain broadhead a blazing 197 feet per second. By today’s standards, such a bow could never kill a deer but with that bow I killed countless deer as well as bear and small game and other critters and I always got a pass thru. I cannot recall a single instance where any game animal ran off with my arrow.

As far as this test goes, as expected, heavier arrows provided more power and efficiency but only to a point. It would appear that the sweet spot that can obtained from this bow comes from using a 9 grain per pound of draw weight arrow even though momentum continued to increase. Regardless of the bow you use, there is an arrow weight that will provide the maximum impact performance and efficiency. That being said, arrow lethality is not any one single factor but is a combination of several factors.

1. Shot placement (no amount of math will make up for a poorly placed shot)

3. Impact force (KE and MO)

None of this will come as a shock to traditional bowhunters using a stick and string. They have long known the advantages of high arrow weight to draw weight for penetration but the modern compound bow market is stuck in the speed fad and all advertising seems to be based on feet per second as if that were the end all and be all of bow performance. Speed is only one part of the equation. But the current fad is speed and from a bowhunters perspective we consider speed when thinking in terms of things like yardage estimation but rangefinders have all but negated that. Another consideration for arrow speed is the effect of speed in regards to a deer’s ability to jump the string but please consider the following. If your bow provides the maximum in performance with a heaver arrow at 250 FPS vs 300 FPS you are still better off with a more efficient performing bow/arrow because a few FPS means nothing to a deer’s ears since sound travels from your bow to a deer at 1,126 feet per second. A few feet per second of bow speed pales in comparison to the speed of sound. Even with the fastest bows on the market at 360 FPS, the sound of your intentions will reach the deer more than 3 times faster than your arrow will.

So how does the hunting archer test and evaluate and experiment to get increased performance for his bow? You will need a chronograph. If you don’t own one, perhaps your local archery club does (another good reason to be affiliated with a local club). You can also visit a local archery dealership and for a few dollars and with an assortment of field tip weights, weight washers, weight tubes, weed trimmer line and even masking tape to get you to the weight you want, you can find out the sweet spot that will give you better performance from your bowhunting gear. Perhaps you can maximize performance with a few weight collars and/or a weight tube inside your arrow. Using weed trimmer line to boost your arrow weight which reminds me of a story. I was contacted by a whitetail bowhunting friend who planned to go out west on an American bison hunt and he was looking to optimize the output from his 70 pound compound. He knew his 375 grain whitetail arrow was not going to cut it for such a big animal. After a little experimenting we ended up with brass inserts, a 200 grain broadhead and 4 lengths of weed trimmer line inside his arrow which brought him to a hefty 700 grain arrow (10 grains per pound of draw). The performance and penetrating ability of his arrow ended the life of a 1,700 Bison at 35 yards. His arrow passed through both sides of the chest of the roughly 3 foot wide beast. This might be a bit extreme for thin skinned whitetails but hopefully you get my point. Maximizing a bows output puts the odds in your favor for making a quick, clean, good penetrating and ethical kill regardless of the size of your prey. Personally I find it objectionable for a game animal to run off carrying an arrow not to mention the increased difficulty in blood trailing a deer with no exit hole. If that happens, there was a breakdown in at least one of the three points of arrow lethality mentioned above.

If speed is your thing, the answer is easy, shoot an IBO weight arrow weight but I caution using an arrow lighter than that since less than 5 grains per pound of draw risks voiding your bow’s warranty so be aware that too light an arrow comes with some risks. There were other things I noticed as I increased arrow weight. Bow noise and vibration felt in the hand dropped as arrow weight increased. Both are a good thing for bowhunters. Also, there was a noticeable increase in penetration into my target as I reached 11 grains per pound of draw due to the ever increasing momentum. This pondering turned out much lengthier than I originally anticipated, thanks for listening. I hope you were able to pull something of value from it.

beaverman05

Posts: 35
Joined: Sun Aug 21, 2011 5:10 pm

Re: Getting the most from your bowhunting setup

Great post!!

This maybe a dumb question but here goes anyway. Are your arrow weights with or without braodhead weight included?

I'm just wondering because now I'm trying to figure out what my setup is! I shoot 70# draw weight with the golden tip pro hunter arrows that are 29" long I think(sorry at work right now so I couldn't messure). According to golden tip website my arrow would be just about 8.5 grains per inch. I shoot 125 grain broad heads! And I tested my fps. And it was faster then I thought at an average of 275 ft/sec. According to your charts this should be a good setup for me then.....right???

kellory

Posts: 2698
Joined: Tue Jul 26, 2011 3:01 pm
Location: Ohio

Re: Getting the most from your bowhunting setup

nicely done.
The only real difference between a good tracker and a bad tracker is observation. All the same data is present for both. The rest is understanding what you are seeing.

scottflesher

Posts: 605
Joined: Sun Oct 11, 2009 3:44 pm
Location: SE Ohio

Re: Getting the most from your bowhunting setup

excellent post retch. Not sure that some get as involved as you do, however i'm glad that you took the time to share the quanifiable results of your study. It can only make us better more aware hunters.
Thanks again

Joel Spring

Posts: 73
Joined: Wed Oct 13, 2010 10:42 am

Re: Getting the most from your bowhunting setup

Excellent research and a very informative post.

Being a bow hunter and a handgun hunter, I see a lot of these misconceptions cross over into that hand-loading world, too. It's all about speed, less about lethality, much to everyone's detriment.

I shoot a .44 mag mostly for deer hunting, and the load I use is considered "moderate to mild". I see some of the smoking-hot (and painful!!!!!) hunting loads that guys are shooting in their handguns and just have to laugh. What they forget is that a 240 grain bullet doesn't have to be flying at light speed to break a mature deer's shoulder....IT'S a 240 GRAIN BULLET!!! Same concept.

I've always liked a nice, heavy arrow, and good penetration. Better than an arrow going Mach 5 and disintegrating on contact if it happens to nick a shoulder blade.....

Good stuff!!
Joel Spring
Longtime Deer & Deer Hunting Contributor
ruabirddog@aol.com