Arrow weight and penetration confusion

[270WINCHESTER]

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!

[Bergerboy]

Originally Posted by 270WINCHESTER

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?

[KrisRD]

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.).

[Timberdoodle]

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?

[calgarychef]

Originally Posted by Timberdoodle

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.

[Lefty-Canuck]

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