Arrow weight and penetration confusion
 

Need some wisdom to try and clarify my confusion here. So for the most part it seems that people agree that heavier arrows will result in greater penetration then lighter arrows. correct? If so here is what I am now confused with. I was shooting two arrows side by side. Both VAP TKO's, same length both shooting 100-grain points. One set a 300 spine the other a 400. The 400 spine arrows had a total weight of 386 grains. The 300 spine arrows a total weight of 486 (the additional 100 grains came from inserts. So in theory the heavier 300 spine arrows should have greater penetration correct? However, from 30 yards they were just barely poking through a new block target, while the lighter 400 spine arrows were a good 2 inches through. So why is the lighter arrow getting greater penetration? The difference in the spine shouldn't have that much effect, or does it?
I'm shooting a PSE xpedite, 29" draw at 60lb . Not a slow bow by any means and from what I have heard from others and researched myself a 300 spine arrows seem more along the correct lines then a 400. Does 400 not seem under spined for this setup or??

Any advice on the subject would be greatly appreciated.

Thanks!

Do they have the same outer diameter and surface finish?

I believe the VAP TKO's come in a 350 spine which would seems to be the closest match to your draw weight/length. The 300 spine seems a bit on the stiff side for your setup. I shoot 70 lbs with a 31" draw with 300 VAPs and they have tuned well. Have you had any issues tuning the bow with either of the arrows? Tuning could be part of the penetration issue.

If the 300s are coming off the bow a bit crooked, they may be losing more speed that you'd think or impacting the target at a bit of an angle.

Overall, I would expect more penetration from the heavier arrows if everything else about the is the same (shaft diameter, finish, field tips, etc.).

Momentum = mass x velocity. In order for the heavier arrow to penetrate less, the velocity would need to be a decent amount less, or there would need to be another factor at play (such as friction). The OD of the 300 is slightly larger than the 400 (.242 vs.231), which could reduce the penetration on a target that stops arrows by friction. Do you know the difference in arrow speeds?

I would suspect that the tuning is slightly off, introducing an additional friction component if all other factors (same shaft materials, field point styles, etc.) are the same. Do both bare shafts fly straight & parallel to each other out at 20-30 yards?

Great post!

But.... this conversation will quickly devolve, there’s no agreement between the light and fast s heavy and slow thinkers.

All I know is you don’t shoot a cape Buffalo with a 22-250 (light and fast) you use Something like a 416 rigby (heavy and slow).

All of the big animals that I’ve gone after have included some heavy thinking about heavy arrows and how to best tune them for perfect flight.

I shoot the heaviest arrow I can at 285fps, currently that puts me at 440gr, I passed through an elk at 87yrds... that’s all the proof I need.

LC

How long are your arrows? According to Victory's chart regardless of length of arrow for your bow speed and draw weight 350 is the stiffest arrow they recommend. I would likely guess the heavier arrow isn't flying very well which is slowing it down. Just my guess though

I believe your arrow weights are off a bit. The extra speed (40+fps) AND the smaller diameter 400 shaft would give it the edge in penetration. KE values are close to the same. The IBO of your bow would suggest a stiffer arrow than the charts indicate, all depends on how they tune though.

KrisRD has the right answer. The 300 spine arrow is to stiff for the OP's set up. If he wants to shoot the 300 he will need to retune his bow. Even then proper arrow flight may not be possible. You ca not shoot 2 different spined arrows out of a bow and have both tune properly. Pick one make and style and spine of arrow and shoot it. That is my advice for what it is worth.

Video regarding smaller diameter arrows.
https://youtu.be/yM8hVULuNkg

Thanks for the advice guys!
I decided to strip the fletching and do some bare shaft shots to get a better look into things. The 400's had ugly tears in all nock positions while the 300s were bullet holes once nocked tunned. So now even more confused however none the less will likely shoot the 300s due to the clean bare shaft through the paper. Is this a good or bad idea or should I go to a 350 spine and re-tune? thinking of fletching up some of the 300s tonight and see how they group with the bare shafts.
In regards to the penetration. Both the 300s and 400s are making it an inch or two through a new block target. So even if the 400's do have a slight penetration edge over the 300s, its not like the 300's are lacking penetration by any means

From the way your explaining things I’ve got my doubts you know what to do with those bare shafts but regardless you’ve got to tune the bow for each arrow. Telling us the .300’s shot well and the .400 didn’t doesn’t mean much without a lot more information. My guess is you could make either tune but a .340 would be what I would buy for that bow.
Quick and short version, properly tuned and all else being equal, heavier always penetrates animals further. Your block target uses friction to stop arrows which doesn’t mean anything in regard to penetration potential with an animal. It does mean an arrow can get further into the target before that friction gets it stopped which explains some of your observations.
I’ve got no interest in explaining much but there is a plethora of information available online and heavier breaks bone and penetrates animals further then light. I’ve never reliably broken shoulders with any 400ish grain arrows.
I’ve done bone penetration tests on both animals and green bones. I’ve hunted everything from gophers to water buff with a bow and I can tell you my experience has me shooting heavier then average. Speaking of testing, I used to shoot into a natural sand bank for a target. 400ish grain arrows penetrated about 6”, my 530 grain hunting arrows went in about 12-14” and my 770 grain water buff arrows went in about 35”. I had to dig to find them.

Even more important and often undiscussed is arrow integrity. I torture test my setup from shooting paving stones straight on at 2-3m to glancing them off the butt end of a firewood pile at an angle and if anything fails it needs attention. I can ramp my arrows off of or into anything from a 340 IBO bow with a 30” DL and 80lb draw weight and they won’t fail. That’s worth taking the time to achieve and it’s paid off when I’ve made tough shots. Since I went heavier and properly tuned with tough enough arrows I haven’t had an animal stop an arrow on any shot.

My Alberta setup was 530 grains at 285 FPS and it worked well. No issues with penetration or trajectory.

Good post. Proper arrow flight, footing each end of the arrow, glueing it all together from Knock to head ...these little things add up, to a very tough arrow.

How far away are you when you paper tune 270 W. You should move back as you tune to make sure your arrow is not just tuned at a very close range. I now tune from 8ft to 20yds. Then I tune matching my field points to my broadheads. What I mean is both impact at the same spot no changing your sights to shoot one or the other. A properly tuned set up is a deadly weapon. It is made even better witha good heavy arrow. A side benifit of a heavy arrow is it will make your bow quieter on the shot. It is good to hear you are tuning your bow now not waiting until Sept. first.