Speed vs weight...a followup

[rusty]

Posted the other night here: http://www.rokslide.com/forums/show...eight...recommendations-for-bowhunting-arrows. Had some great responses, and I decided after reading them that hunting with the rig I had wasn't a very good idea.

Went to the local shop here and decided to try swapping out the inserts from 10gr to 100gr brass ones. Shot the bow through the chrony before and after. After all was said and done, found a really significant difference:

Arrow weight: 335->425 grains
FOC: 12%->20%
Speed: Average 294 fps (lower than I thought actually)->264 fps (12% decrease)
Momentum: 14.1 slug-fps -> 15.6 slug-fps (12% improvement)
Trajectory: 3" lower at 20yds, 14" lower at 40yds
KE: 64.2 ft-lbs->65.7 ft-lbs (bow is actually 2.2% more efficient with the heavier arrow)
Noise: Loud and twangy->noticeably quieter

In addition (and most importantly of all), the penetration in the target is noticeably better.

I was sure my draw weight was at 62# last year but I checked tonight and it's only 60#. I would jack this up but I'm pretty sure I'm cutting it as close as is comfortable to the spine limitation of the arrows (26" STL hunter 200s) now.

Everyone's input and advice was much appreciated. I feel a lot better about hunting with this rig now. Thank you kindly!

 

[Jared Bloomgren]

It is a constant battle between deciding what is best. You made the right decision! You are also shooting some great arrows!

 

[RosinBag]

I personally would drop to 50 grain inserts and crank your bow up a little. If you went from 10 to 100 grains, your arrow may have been slightly stiff at the beggining as that is a ton of weight up front. 50 grainers at a higher poundage should be fine on spine, make FOC better, better trajectory and still increase your momentum. Just my thoughts....

 

[Rent Outdoor Gear]

I personally would drop to 50 grain inserts and crank your bow up a little. If you went from 10 to 100 grains, your arrow may have been slightly stiff at the beggining as that is a ton of weight up front. 50 grainers at a higher poundage should be fine on spine, make FOC better, better trajectory and still increase your momentum. Just my thoughts....

I tend to agree - your spine may be too weak now unless you started out with a pretty stiff arrow. I get the best accuracy and trajectory when I use approximately 150 grains in the front of my hunting arrow. When I've used 75 grain brass with 100 or 125's I start getting strange stuff. You've made some nice energy gains and certainly have a quieter and more efficient bow, but too much of a good thing (FOC) can cause some issues. I think a 385 grain arrow is a lot better than a 335 grain arrow and might be good enuff until the next time you need to replace arrows. Then I would consider using a heavier shaft to get the rest of the mass you're after. Use an Easton Axis or FMJ to add the extra beef next time. That will keep your FOC in check and get the deep penetrating mass you're after. Nice analysis by the way - good to see the numbers and that you're doing your homework and testing the results!

Just realized you posted the arrow - I'm not familiar with these... what is the spine?

Coop

 

[rusty]

Spine is .424", but remember these are 26" long. The guy at the shop here figured that if the spine was off the arrows would be throwing left or right at 40, but the impact point was 14" low and directly under the aiming spot. He figured that adding 100 grains was the same as increasing draw weight by 12 pounds, and the Carbon Force chart shows these as good to 75 pounds for a 26" arrow.

Next year I'm going to a proper arrow shaft and higher draw weight for sure. Learning plenty from the forum here!

 

[RosinBag]

rusty your FOC is extremely high, so much it certainly will cost you accuracy. I am no where near the engineer / guru that Darin is, but the numbers up front are off any reasonable chart I have ever seen.

I wouldn't get caught up in the 400 grain number. I shoot a 29" arrow at 415 grains for hunting, but if cut to 26" it would already be down to 395, which would be just fine. Getting 12% better number in momentum and 3% KE isn't mind blowing results for what you potentially give up in accuracy. And when it comes down to it, it doesn't matter how fast, flat or how much momentum if you don't hit what your aiming at.

Your new set up has so much FOC at a slow speed your arrow is going to drop out of the sky as it slows, which it will do quickly.

Your set up would seem more than adequate at 385 grains, 62 pounds. Should put you at about 280 fps, 65 foot pounds of kinetic energy and 14.9 slug-fps, plus you wouldn't lose so much down range trajectory.

There are hundreds of people shooting under 400 grain set ups that kill everything in the lower 48 every year. Arrow in the right place and a sharp broadhead will get it done time and time again.