How to balance arrow weight vs speed for penetration

[TexasStick81]

Terry, I'll have to run more extensive numbers than I did this past weekend to find the sweet spot.  I feel good about the arrow flight with my AD lites and BH's in the no mercy 4 blades.

[LittleBen]

Ok here's my two cents since no one has mentioned it yet.

I gap shoot .... thats right ...say what you will. As a result, the faster the bow the bigger the gap and the longer the point on distance. at 155fps my point on is like 35-45yards depending on anchor point (nock at corner of mouth vs first finger at corner of mouth).

I try and keep most of my bows shooting around 140-150fps ... that usually means about 10-12gpp at my 25"draw length.

I'm sure lighter arrows would kill deer but I like having my bows shoot similarly in terms of gap. No other reason than that.

I'd like to keep the point on to 30yds to reduce the gap and have a point on that correlates to a reasonable max hunting distance ... .probably going to have to move the anchor point again though because too much arrow weight can also get ridiculous.

[LittleBen]

Sorry for the double post my browqser freaks if I try and edit ...

But to Terry ... I recently chronoes a 42# bow with arrow weights of 465gr up to 665gr ... so maybe 11gr/lb to 15gr/lb and the momentum and KE was still rising. I agree from a hypothetical standpoint that eventually you will see no more gains but you'd have to be shooting telephone poles.

[JimB]

I've only chronoed up to 14 GPP but at least up to that point,momentum was going up.

Here are some figures for a 51# Bear TD with Rose Oak limbs.
1.714 gr arrow,155 fps,14 GPP,momentum .49
2.619 gr arrow,165 fps,12 GPP,momentum .45
3.530 gr arrow,175 fps,10.39 GPP,momentum .41

Going from lightest to heaviest that's a 12.9% loss of speed and a momentum increase of 19.5%

Fred Bear did impact testing up to a ridiculous 18 GPP and found impact increase all the way up to there.But,he liked 9-10 GPP,because of the balance that we are talking about between trajectory and penetration.He also took very long shots at game,at times.

I think you just have to decide where your personal balance point is and what kind of trajectory you need or like.

[TxAg]

Zane, you probably already know this but just in case someone else would like to see it, here is the momentum formula to check your set up.

Momentum = grains of arrow weight / (divided by) 7000 X (multiplied by) fps. Then divide answer by 32.

[Bill Carlsen]

It is also about where the weight is. I think it is better up front than if it gained via some sort of weight tube. But a razor sharp head flying on a finely tuned perfectly straight flying arrow trumps everything else.

[JimB]

I listened to some audio of Ed Ashby speaking at the P+Y convention in Dallas(On tuffhead.com)and he was asked about what his findings were on diminishing returns.He said that on straight limbed long bows they found it at about 10 GPP but on highly efficient hybrid bows it could be at 15-16GPP.

He also reminded people that diminishing returns does not mean there is no increase,just that the increase slows down.It wasn't that long ago that I used to think it meant the increase stopped or went backwards,but I learned that that is called negative returns.

There are both audio and a couple videos from the talks,over at Tuffhead.I would like to have been there.It would have been nice to throw out some questions.

[TexasStick81]

Guys I'm really enjoying the conversation.  I appreciate that for the most part people on this site can have different opinions and yet find value in others' perspectives.  It's a pleasure to just listen to guys with great experiences. Keep em coming