Archers Advantage - How accurate on FPS and thus Spine Selection?

[philcox]

My AA setup. What does not make sense to me is how the arrow weight and speed change when selecting Tied Loop or Jaws. Is it adding the .5gr for the D-Loop on the string?

Speed calc (since sight tape is right on, I have to believe this is correct)


With Jaws Release


With Tied Loop

 

[philcox]

My speeds were a little slower than chrono but tapes are dead on. I used the sight in method and my chrono was 286 but with sight in method said I was actually 283.8 and that tape works perfect.

What specs are you shooting? DL, #, Arrow weight, etc?

 

[Billy Goat]

My AA setup. What does not make sense to me is how the arrow weight and speed change when selecting Tied Loop or Jaws. Is it adding the .5gr for the D-Loop on the string?

Speed calc (since sight tape is right on, I have to believe this is correct)
View attachment 393612

With Jaws Release
View attachment 393608

With Tied Loop
View attachment 393609

You likely have 1" overdraw. Most bows do.

I can't tell you why it changes, it's not enough to matter.

Like I said previously, lots of things can alter speed. You are shooting a pretty tall vane, also shooting at 80 you might float your anchor a little and that changes your relative impact.

Since you have that screen shot, go to your bow setup and alter your current speed to around 248. See what that shows you with spine.


If your tape is accurate, that's all you need there. Just I don't think it's showing everything. With that bow being rated past 340 fps, I think it's going to be weak with a 300 and 275 on the front at 28 5/8". Now, get that arrow down to 27.5" and I think it would work.

 

[Kyle Wheeler]

What specs are you shooting? DL, #, Arrow weight, etc?

30 inch draw, 65# with 80% letoff, 435 grain Easton 6.5 match arrows. Shooting a Matthews VXR with Tommy Hogg and Carter Wise Choice. Really enjoying it!

 

[Mighty Mouse]

The 262.55 FPS is over 24 fps more than my measurements give me from AA (238.2). I am guessing that is the difference in the AA "stiff" and Pinwheel "weak"

Pinwheel likely is being a bit optimistic on the speed calculation. I've noticed that it tends to overestimate speed for bows with rotating draw length mods shot below max DL.

But I also think 238 fps is unrealistically low for the bow specs and arrow weight you listed. Using a measured pin gap to infer launch speed seems ripe for error for the reasons Billy Goat mentioned above.

I would personally use chronographed speed rather than calculated speed to assess arrow spine.

 

[philcox]

You likely have 1" overdraw. Most bows do.

I can't tell you why it changes, it's not enough to matter.

Like I said previously, lots of things can alter speed. You are shooting a pretty tall vane, also shooting at 80 you might float your anchor a little and that changes your relative impact.

Since you have that screen shot, go to your bow setup and alter your current speed to around 248. See what that shows you with spine.


If your tape is accurate, that's all you need there. Just I don't think it's showing everything. With that bow being rated past 340 fps, I think it's going to be weak with a 300 and 275 on the front at 28 5/8". Now, get that arrow down to 27.5" and I think it would work.

Some questions (I should know, but I don't):

1. What is overdraw? How would I know if I have it, or what it is?
2. So even with a 300, you think that might be weak, and not too stiff? Is that because of the tip weight, not necessarily the overall arrow weight? Is there a good way to see if weak/stiff/etc.? I get nice alignment on paper with my fletched arrows at 30 (no tailing)

Perry from AA told me to use "Tied Loop" and Chrono (not measure) for Spine Selection, and measurement for Sight Tapes. That was new to me.

Since I am a tinkerer, learning all this it fun too.

 

[philcox]

Pinwheel likely is being a bit optimistic on the speed calculation. I've noticed that it tends to overestimate speed for bows with rotating draw length mods shot below max DL.

But I also think 238 fps is unrealistically low for the bow specs and arrow weight you listed. Using a measured pin gap to infer launch speed seems ripe for error for the reasons Billy Goat mentioned above.

I would personally use chronographed speed rather than calculated speed to assess arrow spine.

That last statement is what Perry from AA said to do as well.

 

[Holocene]

The AA sight tapes have been a great start for me over the years. The software math is really good if you are meticulous with your inputs. I mean grain weighting components, putting your arrows through the chrono and overriding AA's suggested value, actually measuring peep and sight distances. But little things such as vane offset/helical choice and how much glue you dabbed on things seem to be little variances that show up at 70+ yards.

So, I usually print an AA tape on sticker printer paper and select the format that shows lines for every 5 yards -- not every 1 yard -- and ground truth that tape at the range. Meaning, over multiple sessions and during broadhead league I'll shoot the tape and put little pencil marks for my actual yardages. At distance, these start to creep by 1, 2, 3 yards.

If you shoot fixed blade broadheads, the sight tape variances will grow more than mechanicals because of the extra drag fixed blades create. For example, my SEVR mechanical heads shoot about 6" higher at 80 yards than my QAD Exodus.

To add another level of fussy, your tape can change depending on atmosphere, a factor not included in the AA formulas. Another reason to ground truth your tapes -- where you intend to hunt/shoot.

I've heard that at events like Redding, it's the guys with the best tapes that win. Lots of people are fantastic shooters, but those little 1-3 yard tape variances can bite you, at least at distance.

 

[Billy Goat]

Some questions (I should know, but I don't):

1. What is overdraw? How would I know if I have it, or what it is?
2. So even with a 300, you think that might be weak, and not too stiff? Is that because of the tip weight, not necessarily the overall arrow weight? Is there a good way to see if weak/stiff/etc.? I get nice alignment on paper with my fletched arrows at 30 (no tailing)

Perry from AA told me to use "Tied Loop" and Chrono (not measure) for Spine Selection, and measurement for Sight Tapes. That was new to me.

Since I am a tinkerer, learning all this it fun too.

Overdraw is how far behind your grip, or berger the rest is. They aren't talked about a whole lot anymore, it use to not be uncommon to have a 3 or even 4" overdraw, now they are a little scarce.

The tipweight is what really pushes an arrow spine, and you are about double the tip weight of more or less normal arrow.

 

[philcox]

So using the "chrono" I get 252fps, using that in AA for spine selection, and I get Optimal Spine for the 300. Which makes sense. Thanks for all the help. I think I am getting this dialed in.

 

[Marble]

I would put a broadhead on and see how it shoots vs the field tips. I think this is your end goal anyways correct? How that broadhead fly's?

I went through a similar process and built some arrows that "shot well", but not like I normally shoot. When I shot a broadhead through it a few weeks before season, man it was way off. Like almost missed the yarget off. I was shooting a 345 ibo bow, 340 spine with 200 up front. 28.5 DL.

After the season I revisited my set up and built a set at 300 spine, put 50 grain HIT up front instead of a 75 and ended up close to the exact same TAW. This time the broadheads shot with field points out to about 50 to 60 yards. Then they were just a slightly low.

The arrows group much better now.

Every set up is slightly different so this is just anecdotal info just to confuse you a bit...

Sent from my SM-G986U using Tapatalk

 

[philcox]

I would put a broadhead on and see how it shoots vs the field tips. I think this is your end goal anyways correct? How that broadhead fly's?

Yep. I did this. Seems that they fly similar. Archer is more of a variable than the setup.

I did a "cold bow" at 30 yds, just to say "what would it have been like if I were hunting today?" So now to do that over and over out to my MER.