I want to just clear something up in my mind, and maybe for others as well.
I have read alot of information where heavier arrows are supposedly better hunting arrows....why? I understand that the higher ft/lbs energy arrow will be the better for hunting purposes....not so? In my mind a faster, therefore flatter trajectory arrow, should give better penetration,due to its straighter flight at point of impact with target. (ok this is assuming the shot is across level ground at a broadsde animal)
Now see this comparison I have done with one of my setups:
Mathews Drenalin bow, 27inch draw length, 69# draw weight, 398gn arrow
398gn arrow - 62.3ft/lbs energy 265 ft/sec speed
428gn arrow - 62 ft/lbs energy 255 ft/sec speed
500gn arrow - 59.5ft/lbs energy 231 ft/sec speed
Its evident that due to the speed loss, the energy is also reduced. There are other factors, like broadhead type, which may affect arrow flight at hgher speeds, which will make heavier arrows a better option. I use Piston Points which give me excellent flight....also remember that at 27inch drawlength, I opt for lighter arrows for better speed.
According to the heavy arrow proponants, resistance to penetration is a formula that increases by the square of the velocity of the projectile, not the mass of the projectile. The faster the velocity, the more the resistance to penetration. Therefore an arrow that derives it's energy largely from speed rather than mass will slow down quicker than an arrow than an arrow that that derives its energy largely from mass.
Shoot a fast carbon arrow into water and see how fast it slowsdown, shoot a slow heavy fiberglass fish arrow into water, and you get lethal penetrationquite deep.
i'm shooting approximately 450 grains (weight includes vanes, nock, tipand shaft) at 270 f.p.s. which gives me the kinetic energry of around 75 and is considered enough to kill the largest game, i.e. cape buffalo. you can take someone shooting a lighter arrow at 300+ f.p.s. and they will not have the penetration i have with the heavier arrow.
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There's a few factors I'd consider, but the bottom line is....."I" believe mass weight (to a point) is your friend. If you had to achieve this with a large dia. shaft, though....I might change my tune.
Flatter trajectory, at known distances, is NO BENEFIT. Given the information above (and assuming I'm hunting whitetail deer and smaller game), I'm shooting the heavier arrow.
IMO, the best thing a bowhunter can do to ensure he gets maximum penetration......is shoot a razor sharp broadhead from a well-tuned setup. At the distances I hunt, an arrow with a lot of mass weight is my friend.
Ask yourself this, Is it easier to stop a sports car going 75mph or a bus going 55mph. A heavier arrow once in motion is harder to stop then a lighter arrow plain and simple meaning better penetration. Heavier arrows also maintain downrange speed at a higher rate then the lighter arrows meaning highe KE downrange then specs show on the chrono shot at 10yds or less. That is why recurve shooters typically shoot heavier arrows that are not shooting higher speeds yet are able to get passthroughs on large animals.
I shoot ~565 grains at around 265 fps. On one of my spectacular misses last season, I sunk a 1 3/4" Grim Reaper almost 4" into a white oak. For me, I'll take the heavier arrow every time.
The trajectory point GMMAT makes is good too. If you know your distances, you can pick your spot and do just fine. Bows that now advertise 1 pin to 40 yards bug me because it is license to not practice at distance.
2007 Bowtech Commander 70# @32"
Spot-Hogg Hunter Hogg-It 5 Pin
Easton Full Metal Jacket Camo 300
Grim Reaper Razorcut
Grizz Trick 125
Summit Goliath SS
Not getting into the heavy verses light argument but I challenge you to double check your numbers with actuall tuned arrows for each arrow weight.They seem a bit off from the thousands of setups I have checked over the years,and what most everyone else has seen as well.
You also have not even considered momentum.
But,as a side note,trajectory advantages are never what they seem.
Oh,and for the record,I use relatively light arrows.[:-]
Let's assume that the broadhead and diameter of arrow are constant...
Energy comes from weight and speed...But, you don't really have much difference in the speed from the slowest arrow to the fastest...I see this alll the time in muzzleloading, folks want to argue about a few fps when all that fps does is makes the projectile fly a little flatter...
I notice you shoot a pretty short arrow, I'd opt for the heavier oneto give you more weight...
Now, I'm not like most bowhunters...I shoot a bow that's pushing 20 years old because I still shoot fingers...I'm also 6ft 5...So my arrow length is 32 inches...I still shoot aluminum and use 125 heads...
Even with this old, slow setup, it shoots flat enough to use 2 pins out to 30 yards and the arrow exits on lung shot deer...
Momentum is the key physical factor that you have overlooked. Here is a calculated momentum for your weights that you have listed. For this im going to use all of the same arrow characteristics (fletching length/height/OD of arrow shaft/shaft length)so the momentum calculatation will be of equal testing.
here is the momentum (lb-sec.) that your 398gr. arrow at 265fps provided. (0.4676332357896604)
428gr. 255fps (0.4839052939611599)
notice that the momentum continues to rise as you add weight but lose speed...
KE is NOT what makes an arrow pass thru. It is the impact that you arrow gives when it FIRST hits an object. KE does NOT mean that you are going to get good pass thrus.
An arrow needs momentum to get a pass thru. not so much KE. My 101st Airborne that i used to have would shoot a 308gr. arrow at 320fps. It would shoot my hunting arrow which was around 415gr. at 285fps. The KE was really close, but would you want to use a 308gr. arrow hunting??? Yes it may hit the deer with X amount of KE, just as the heavier arrow did, but it would stop so much easier that the heavier arrow since it had the weight to continue to push it through the deer.
Like TFOX said, im not here to preach heavy or light, b/c ive killed deer with both, just stating some facts. Shot placement is key
Oh yeah, and the distance in drop between 0 and 30yds for the same setups...
398gr. 23in at 30yds. 71in at 50yds
428gr. 26in at 30yds. 75in at 50yds
500gr. 31in at 30yds. 90in at 50yds
That may seem like quite a bit but think about it... Between the lightest arrow and the heaviest arrow there is only 8in of difference in drop at 30yds. When your looking at a target at 30yds, 8in aint a whole lot
Now to the site pins... I dont have a way or the time to calculate your pin gap, but all you have to have is a program like AA or TAP or OT2 (archery calculators) to figure it out by measuring your peep to arrow distance at full draw, and your peep to pin distance, along with your arrow weight/length/fletch etc. etc... IF you were to calc. those, im sure you would find that the difference in pin gap is very minimal compared to what most people think...
either way, a well placed shot is what it is. You dont have to be a genius to do that one[8D] Most setups nowadays are SOOOO overly capable that it doesnt even matter, SO.... shoot what you feel comfortable with.