Remember, once you release the arrow, it begins losing speed, energy and momentum immediately and continues losing it as it cuts through the wind resistance, heading downrange. Since we're talking about crunching numbers, I plugged your numbers into the ballistics calculator over at
www.bowjackson.com and here's what I came up with, at 10 yard increments.
Speed, KE and momentum (in pound/seconds)figures for your 314 gn arrow at 269 fps:
0 - 269 50 .3745
10 - 264 49 .3676
20 - 259 47 .3611
30 - 255 45 .3543
So, over 30 yards your 314 gn arrow loses 14 fps in speed, 5 ft lbs ofKEand .0202 pound/seconds of momentum. In percentages, 5.2% loss of speed, 10% in energy and 5.4% in momentum
For your 398 gn arrow:
0 - 244 53 .4306
10 - 241 51 .4244
20 - 237 50 .4186
30 - 234 48 .4126
That arrow lost 10 fps, 5 ft lbs and .0180 pound/seconds in momentum. Or 4% in speed, 9.4% in energy and 4.2% in momentum.
The heavier arrow retained it's speed, energy and momentum better than the light one, which means it retained more penetration potential. Even more important though, the heavy arrow still carried as much KE at 20 yards as your light arrow had at the bow!
At 30 yards,the 398 gn arrowhas only2 ft lbs less energy than the light arrow started out with, and also had more significantly moremomentum than the light arrow had at the bow.
Now, those losses come solely from the arrows cutting though thin air. If the light arrow can't penetrate AIRas well as the heavier one, wouldn't it stand to reason it also can't penetrate a deer's chest cavity as well?
Since increasing your total KE is not going to happen without going to a different bow or increasing your draw weight dramatically, I think the best thing to do is to optimize what KE you ARE getting by using the heavier arrow.
If the decision is between getting the arrow to the deer a few microseconds sooner or increasing the arrow's penetration potential, I know which I'd choose. And I'd alsoecho the suggestions aboutaiming to keep the arrow a little further away from the bones in the shoulder.
