Two bowhunters with the same draw lengths shoot new compounds set to different peak weights, one 51lbs and the other 70lbs. Who’s got the most power? The answer may surprise you.
“How much weight do I need to shoot a deer?” This is the most common question I am asked by prospective bowhunters. I used to reply “Shoot as much weight as you can comfortably handle” but I have stopped saying this now. Instead I say “Shoot the weight you can maintain your accuracy when shooting all day”. The same but different.
Most “good keen blokes” shoot too much weight, they are over-bowed. Some by as much as 10lbs, but most don’t even know it. The problem is often not immediately apparent, only showing itself when fatigue sets it. When out in the field you are unlikely to be too tired to draw your bow although I heard of one tragic case of this occurring. I was talking to a US hunting guide who had taken an older hunter out after elk in Colorado. In preparation for the hunt the client had purchased a 70lb bow for the big-bodied bulls he was expecting to shoot. This was ten pounds heavier than the bow he used whitetail hunting. At the end of their second day an outstanding bull presented them with a perfect broadside shot at only 20 yards. Unfortunately the long days on the hill and the thin air at 8,000 feet took its toll and the brand new bow was unable to be drawn back allowing the bull to dodge the proverbial “bullet”.
“Only drawing 39lbs pounds my Wife Carol killed this 450lb red stag with one arrow. The Helix broadhead penetrated both sides of the ribcage. The stag only travelled 61yards before dying.”
Practice is when the damage is done to those who are over-bowed. Most bowhunters I know will empty their bow quiver retrieve their arrows and repeat the process. The first 2-3 arrows should be no problem however on the 5th and 6th arrows the bow will be harder to draw. This gets worse the more arrow shot in a session. As soon as the bow becomes hard to draw then the focus drifts from the shooting the bow to getting the damn thing back! Not good for your technique and long-term success and enjoyment of the sport.
Now most Kiwi males don’t take kindly to being told they are not as strong as they think they are so I don’t tell them that. Instead I tell them of how much more game they will shot with a lighter poundage bow, how quiet and accurate it will be. This works well, because it is true, on new bowhunters but is a harder sell on those who have been shooting a while.
The train of thought here has been the more the better, especially with those bowhunters advocating shooting high poundage (over 80). This is so they can ensure they get enough penetration on large bodied animals. The logic behind this makes perfect sense as the more energy an arrow has the better it will penetrate (with the same broadhead and same point of impact) than one with less. Where this logic falls over is when it is applied to shot placement. I have heard some bowhunters say they want to be able to take a shot from any angle and rely on their heavy poundage bows to get their arrow through into the vitals. This is simply wrong, very wrong. There is no archery set up I have seen which was capable of smashing through the ball joint of a mature deer or consistently penetrate the shield of a large boar to kill it.
Recently we received an email from an Aussie bowhunter who was asking after compounds available in 80lbs. Shop manager Simon Bullivant, who had recently dropped his bow weight from 80 to 70 asked him why did he need an 80lb bow? A one word reply came back, “Sambar”. This guy was from Victoria and apparently the Sambar there needed a heavy bow to kill them. Simon found this to be somewhat ironic as he had recently taken his 5th Sambar for the year, including two mature stags, with his bow on 70lbs, a Mathews MR6. Since then he has dropped his peak weight to 65lbs and killed 6 more Sambar. One a particularly large bodied stag which only travelled 44 yards after it was shot. Shot placement was the key to his success as penetration was complete on all of the Sambar. Simon’s kinetic energy (a calculation using arrow weight in grains and arrow velocity, visit the Easton website to find out yours) was 91.43 and 83.7ft/lbs, respectively. When he was shooting his heavy bow it was set on 83lbs and he was getting a whopping 104ft/lbs, enough for an elephant.
The other theory behind having a heavy bow is you can then shoot a heavy arrow to maximise your penetration. Long has been the understanding a heavier arrow will penetrate further than a lighter arrow. I have heard much debate on this subject, momentum versus kinetic energy. Both sides have good arguments for their cause. While a heavy arrow (10grains per pound of draw weight) may be of some benefit when hunting the African Big Five there is no big game animal in New Zealand which warrants one.
Modern archery equipment is responsible for this. The bows, arrows and broadheads available now, negate the need for heavy set ups.
My current set up is a Mathews Monster 7 with an IBO rating of 342fps. Set on 63lbs it produces 82.55ft/lbs of kinetic energy.
In 1996 I was shooting a 68lb compound which at the time delivered me an impressive 240fps (the Monster shoots 294fps), combined with the arrow I was using gave me 65.25ft/lbs. To achieve the same kinetic energy with the Monster I would have to drop the poundage to around 50lbs, 18lbs lighter than my 1996 bow.
If I were to go the other way, to get 82ft/lbs out of my 1996 bow I would have had to increase the draw weight at least 14lbs to 82lbs. This is almost 20lbs more than I am currently drawing. My 1996 bow was no slug and was one of the fastest available back then.
Why the big difference? It is a combination of vastly improved bow designs in both the raw energy they deliver and the efficiency they are able to pass this energy to the arrow. 10 years ago a fast bow (which were hard to control) were rated at 330fps. In 2012 the fast bows are rated at speeds exceeding 360fps (you still have to be on top of your game to shoot them ok). Bows with speeds around the 340 and 350fps are more user-friendly while delivering a tremendous amount of energy.
Let’s look at three bows with different IBO ratings and see how they compare. There are a few guidelines which I will use to do this. Firstly the IBO rating shoots a 350grain arrow from a 70lb bow set to a 30” draw length. This is how the IBO speed is determined. Secondly we will assume these ratings are accurate and there is no variation in their draw lengths. Thirdly for every pound difference in bow weight, add or subtract 2fps. Finally the efficiency of the bows will not vary with any poundage changes. Their IBO ratings will be 310, 330 and 350fps.
“Shooting my 63lb Mathews Monster my Helix tipped arrow passed through this not so pretty, Sambar stags chest from 30 yards.”
To get 310fps from the bow rated at 310 then it will need to be set at 70lbs. To get 310fps from the 330 bow you will only need to set the draw weight to 60lbs. For the 350fps bow to shoot 310fps then it would only need to be set to 50lbs. Reversing this process the 330 rated bow would need to be set on 80lbs to match the 350 rated bow and the 310 bow you would have to pull an eye watering 90lbs!
So which of our two bowhunters from the beginning has the most power? If the one with the 51lb bow was rated at 350 and his mates bow was rated at 310 then the lighter bow has more power despite the near 20lb difference in draw weight. I suspect he would be the most accurate as well.
Over the years the New Zealand Bowhunters Society has kept records of the average bow weight used by its members to take big game animals with. For as long as I can remember the average has been 70lbs, sometimes a pound or two more but never less until the latest recording period where it dropped to 65lbs. The particular recording period showed animals taken to be in line with other years so the drop in peak weight is an indicator bowhunters in New Zealand are enjoying the benefits of today’s faster bows.
The downside of these fast IBO bows is their design requires the shooter to have a high level of shooting ability. As I have revealed you can drop the poundage of these bows, making them easier to shoot, without compromising performance.
Shot placement options shouldn’t change no matter what combination of poundage, bow design and broadhead. A marginal shot will always be a marginal shot.
Bowhunters today are very fortunate to have these faster more efficient bows available to them. No longer do we have to shoot a heavy bow get a reasonable level of kinetic energy. A lower peak weight will make you more accurate and ultimately more successful.
Article by Kevin Watson