Momentum is the word of the day. A lot of people seem to mix up KE (kinetic energy) and momentum when it comes to bowhunting (or one could say hunting in general, but today let’s focus on archery). KE seems to be the big buzz word floating around nowadays which is great for marketing, but not so great when talking about actual application; it’s only HALF of the equation. Yes speed is wonderful, a lot of compound guys (and gals) love trying to get that max IBO/ATA that their bows swears that they can get to. But how did we go from shooting recurves (which if you hit 225fps that’s SMOKING FAST!) where we were pushing 500-600 gr arrows, to much faster speeds - the arrows are half the weight? What a lot of hunters, especially new ones, don’t really get exposed to nowadays is that other half of the equation of yes your bow is fast, but because it’s faster, it can push more weight faster too. Think about it this way, you drive a zippy motorcycle into a side of a vehicle at around 130mph, and then take a large SUV and drive it into the side of a vehicle going 70mph, what’s going to do more damage? I like to use Fred Bear’s arrow weight calculation, which is pretty easy, take however much draw weight you’re pulling, say 60#, and add a zero to it, now subtract 10%, which would be 540gr. I know what most of you are thinking, “Holy Toledo! That’s a log, no way can my bow shoot that monstrosity without serious drop!”
Well, I hate to break it to you slick, but you know how most people sight their bows in for going at least out to 60 yards or so? The average distance that has been reported for shooting a deer with a bow, is a whopping 15-25 yards. Wait, that’s it? Yeah, that’s it. Consider that next time you really feel the need to sight your 7 pin sight out to 80 yards, on a rig you plan on taking through east Texas where you’ll most likely never get a clear shot past maybe 35. And say if you are taking shots longer than that, what’s the matter, couldn’t get any closer? But in all seriousness, a closer shot is ideal, and of course there’s always some exception, like flat plains shooting.
Now consider this as well, sure you’re probably getting your 8.0gpi arrows with your rear deploying mechanicals into deer at say 30 yards or so and you’re killing them every time. Awesome, but is the arrow going through, or is it just stopping inside of them? You know what’s better than an entrance hole? An exit hole. You know what’s better than that? Pass through. Yes I understand the benefit of a broadhead swirling around inside, causing mayhem is fantastic, but you still have the shaft blocking a fair deal of potential blood loss, where a clean pass through will guarantee a great deal more blood loss which is definitely more beneficial and integral to a quicker death. Now a term that is thrown around a lot is FOC (front/forward of center), which actually effects arrow flight and impact. FOC is essentially a way of saying that there is more weight towards the front of the arrow rather than the back, or it balances more towards the front. This is important because your fletchings on your arrow are made to stabilize arrow flight due to the flex, which can be affected by anywhere from an improperly tuned bow, finger releasing, torqueing the bow, etc. The less work your fletchings have to do to compensate, the faster it will straighten. They do this by spinning the arrow to straighten out the shaft, which if the front of the arrow has a fair deal of weight or is stiffer; it’ll force the back end to balance quicker. To find your FOC just follow these steps:
1) Measure the length of the shaft from the throat of the nock to the end of the shaft, excluding the insert; this is length “L”
2) Using a sharp edge, balance the arrow (including the point) and mark the balance point
3) Measure the distance from the throat of the nock to the balance point; this is length “B”
4) Input B and L into the following formula:
Typically speaking I’d say keep target arrows around 8-12%, hunting arrows 11-15%, but also bear in mind that it is not uncommon for some of the old school bow hunters (and younger ones such as me) to go on up to 30%! This granted is a lot, but just keep in mind, how far you’re trying to go, your draw weight, draw length, your bow’s speed capabilities, etc.
There are so many other aspects of arrow dynamics, such as smoothness of the shaft, what kind of inserts you’re using, your vein selection, nock weight (lighted nocks are heavier, so keep that in mind when trying to achieve a specific FOC), and of course the outside diameter of the arrow itself. Generally speaking I do tend to prefer the micro diameter shafts because it’s less surface area to push through an animal, so it makes for easier penetration, but there aren’t too many really heavy micro diameter arrows out there, usually from what I’ve seen those top out at are around 10gpi (grains per inch). Of course you could cheat this by adding weights into your shaft, to offset FOC and increase overall weight but be mindful that you’re aware of exactly how much weight whatever you’re using is, you need to make sure your arrows all weigh the same. I have used fishing weights, they seem to work okay, but making sure they stay in one place can be tricky if you’ve already put an insert into the arrow, which means you have to go from the back, but using certain kinds of epoxy because it doesn’t bond right way and a long thin device to push it down should typically work as long as you don’t allow the epoxy to seep in through the hole in the bottom of the insert.
Your arrows are an integral part of bow hunting, so just remember there are many things to keep in mind when picking out what kind of arrows you want, and practice and fine tune seeing what works with your particular rig and needs. Like, if you’re only drawing 50# and your bows rated fps is around 300, it’d probably be best not try and launch 700 grain arrows. Tinker around and see what kind of performance you get out of your arrows and remember, practice makes perfect, and most importantly, have fun out there and get yourself a nice rack, and a full freezer.