Density altitude and sight tapes

[sickles107]

You guys don’t have to do all this sight tape stuff. Just back out your limb bolts slightly until your bow shoots to your pins again. Pretty simple.

Doesn't work if you are going from high altitude to low.

 

[Marshfly]

Doesn't work if you are going from high altitude to low.

It does.... unless you are maxed out. haha. But I think most people have the other issue.

 

[HighDesertHunter]

I shoot at home (~3,600') out to 120 pretty regularly. For hunting, I limit my self to 60 yards. I have not seen a full tape change from 1000' to 6500' out to 60 yards. I have not tried longer shots 100+ at other altitudes to see if it is more pronounced. Since you are going to Alaska, I have seen very pronounced changes from heavy rain...

 

[jonesn3]

I started using PCA this winer/spring. Mostly just out of curiosity at first and tried it using the free trail. I ended up paying for the entire year. I found its pretty much spot on for those longer distance shots when other site tape generators seem to break down (at least in my experience). The 2X Marks method with a chronograph initial velocity is pretty sweet, but if you can do the downrange velocity method its faster and either the same results or perhaps slightly more accurate IMO.

I live at El. 1000 ft on the West Coast. The mountains are only an hour drive for me, but all my practice happens at El. 800-1000 ft. I tested out a site tape for a 3D Shoot last month where most shots are +/- El. 8000 ft and 60-90 yd targets are common. I found that anything inside 60 yds was practically no difference compared to my "normal" site tape for at home, 60-80 yds was about a 1 yd cut, and 80-100 was a -2 yd cut, and so on. For 3D shoots at significantly different elevation, I would certainly make a separate sight tape

However, for hunting applications I would just stick to whatever you normal setup is and have mental or written notes on your cuts for your particular hunting elevation. I'm sure if you're hunting CO at El. 10,000 ft it could a much bigger difference. But, for me and with our elk zone being typically under El. 8000 ft max (on average closer to El. 6000-6500), the difference aren't worth a different sight tape. For practical shot distances on animals (inside 60 yds), the difference for my particular sight tape is negligible. I would definitely compare site tapes ahead of time, check it for yourself, then decide. As others have said, probably the most important thing is check POI when you arrive on the hunt to make sure your fixed pins haven't moved during travel. That's just my 0.02.

Here's my comparison between my "at home" site tape and the adjusted tape for my elk hunting area.

 

[180ls1]

I started using PCA this winer/spring. Mostly just out of curiosity at first and tried it using the free trail. I ended up paying for the entire year. I found its pretty much spot on for those longer distance shots when other site tape generators seem to break down (at least in my experience). The 2X Marks method with a chronograph initial velocity is pretty sweet, but if you can do the downrange velocity method its faster and either the same results or perhaps slightly more accurate IMO.

I live at El. 1000 ft on the West Coast. The mountains are only an hour drive for me, but all my practice happens at El. 800-1000 ft. I tested out a site tape for a 3D Shoot last month where most shots are +/- El. 8000 ft and 60-90 yd targets are common. I found that anything inside 60 yds was practically no difference compared to my "normal" site tape for at home, 60-80 yds was about a 1 yd cut, and 80-100 was a -2 yd cut, and so on. For 3D shoots at significantly different elevation, I would certainly make a separate sight tape

However, for hunting applications I would just stick to whatever you normal setup is and have mental or written notes on your cuts for your particular hunting elevation. I'm sure if you're hunting CO at El. 10,000 ft it could a much bigger difference. But, for me and with our elk zone being typically under El. 8000 ft max (on average closer to El. 6000-6500), the difference aren't worth a different sight tape. For practical shot distances on animals (inside 60 yds), the difference for my particular sight tape is negligible. I would definitely compare site tapes ahead of time, check it for yourself, then decide. As others have said, probably the most important thing is check POI when you arrive on the hunt to make sure your fixed pins haven't moved during travel. That's just my 0.02.

Here's my comparison between my "at home" site tape and the adjusted tape for my elk hunting area.

View attachment 732649

Does that account for the temp drop (added drag) and addition of broadheads (added drag) besides the elevation and other factors?

 

[sickles107]

I started using PCA this winer/spring. Mostly just out of curiosity at first and tried it using the free trail. I ended up paying for the entire year. I found its pretty much spot on for those longer distance shots when other site tape generators seem to break down (at least in my experience). The 2X Marks method with a chronograph initial velocity is pretty sweet, but if you can do the downrange velocity method its faster and either the same results or perhaps slightly more accurate IMO.

I live at El. 1000 ft on the West Coast. The mountains are only an hour drive for me, but all my practice happens at El. 800-1000 ft. I tested out a site tape for a 3D Shoot last month where most shots are +/- El. 8000 ft and 60-90 yd targets are common. I found that anything inside 60 yds was practically no difference compared to my "normal" site tape for at home, 60-80 yds was about a 1 yd cut, and 80-100 was a -2 yd cut, and so on. For 3D shoots at significantly different elevation, I would certainly make a separate sight tape

However, for hunting applications I would just stick to whatever you normal setup is and have mental or written notes on your cuts for your particular hunting elevation. I'm sure if you're hunting CO at El. 10,000 ft it could a much bigger difference. But, for me and with our elk zone being typically under El. 8000 ft max (on average closer to El. 6000-6500), the difference aren't worth a different sight tape. For practical shot distances on animals (inside 60 yds), the difference for my particular sight tape is negligible. I would definitely compare site tapes ahead of time, check it for yourself, then decide. As others have said, probably the most important thing is check POI when you arrive on the hunt to make sure your fixed pins haven't moved during travel. That's just my 0.02.

Here's my comparison between my "at home" site tape and the adjusted tape for my elk hunting area.

View attachment 732649

This is exactly what I was after. Actual data or experience in drop differences at 80yd from significant DA change. Thank you for sharing.

 

[jonesn3]

Does that account for the temp drop (added drag) and addition of broadheads (added drag) besides the elevation and other factors?

No, not at the moment. The comparison I showed is just adjusted for atmospherics (elevation, temp, baro, humidity). But that could be "easily" updated for broadheads by truing the arrow+broadhead BC with updated downrange velocities. That would be an interesting test. Certainly there will be differences with the broadhead attached, but how much difference would there be? Again, that'd be a good experiment. As an aside, I did test the downrange difference in extreme helical fletching vs. minimal offset. There was only a 1-1.5 fps difference at 70 yards and my shooting isn't good enough to see a significant difference in groupings at that distance.

Broadhead tuning is next on my "to do" list for pre-season prep, so I will report back if I end up testing that out.

 

[MattB]

I sighted in in western WA, at 400’ elevation, then moved to ID and at 5000’ my sight take was hitting high. At 20 yards i was shooting 3” higher than in WA. Im shooting a 440 grn arrow at 290fps. Your vane configuration and drag will make a difference on how it responds to air density, so its hard to calculate that. You will need to just afjust your sight when you get there. You should be able to move your sight to where your 20 is hitting center again, then while keeping the sight in the right spot, move the pin indicator on your tape to match up with your 20 again… should still be pretty close.

Something likely got bumped while you were moving, no WAY the elevation resulted in a 3” difference. Likely not even at 90 yards.

 

[MattB]

Yeah. Your bow is shooting faster. Just make it a little slower. Haha.

The bow isn’t shooting faster, the arrow just isn’t decelerating as quickly over distance because the thinner air offers less resistance. Sorry about a nit, but I think it might clarify what is happening for some folks.

 

[Marshfly]

The bow isn’t shooting faster, the arrow just isn’t decelerating as quickly over distance because the thinner air offers less resistance. Sorry about a nit, but I think it might clarify what is happening for some folks.

You’re right. Good catch.

 

[nphunter]

This is just one more thing to worry about that 99% of people shouldn't. Most people don't even make a sight tape for their broadheads, I would guess 1/10 or less of the shooters on Rokslide actually build their site tapes shooting broadheads instead of field points. A broadhead will make more of a difference on your shot than air density at distance.

 

[Pramo]

I live at 500 ft and have noticed no difference up to 7500. Once I get to 10,000 things are different and I have to back off poundage or raise my sight I'm off 2-3 inches at 40 yards

 

[sickles107]

This is just one more thing to worry about that 99% of people shouldn't. Most people don't even make a sight tape for their broadheads, I would guess 1/10 or less of the shooters on Rokslide actually build their site tapes shooting broadheads instead of field points.

I must be a one percenter, because my tape for home was determined by shooting broadheads at 100.

A broadhead will make more of a difference on your shot than air density at distance.

Please explain more about presenting such a generalized statement as fact. Does going from a field point to a sevr 1.5 drop more at 80yd than going from 10k DA to 0 DA?

You surely must already know the answer to my original question.

 

[deglazed]

good info! thanks for it

 

[z987k]

For those that have been following shoot 2 hunt / form, they talked about using density altitude as the only variable for air density in a ballistic calculator. I have been using this the past year or so with good success with a rifle.

Has anyone used this same concept for archery sight tapes? I don't have much experience shooting at differnt altitudes. Been shooting all summer at 5k elevation, ~75 degrees, ends up around 7kDA , comfortable with broad heads at 80.

Heading to Alaska this fall, right around sea level, depending on temps could be near 0 DA. I plan on buying a cheap atchery target when I land, though trying to get an idea how off my sight tape could be at 80.

I almost guarantee you'll have a below sea level DA. If you're at sea level and fall Temps it'll likely be -2000ft or more below.
Our pressure changes a lot to. Nothing to see pressure below 29.00, might even be a nice sunny day. And a week later it's 31.00 and raining.

 

[jonesn3]

This is exactly what I was after. Actual data or experience in drop differences at 80yd from significant DA change. Thank you for sharing.

For me, I would prefer not create a unique and different site tape for broadheads. I’d rather keep the same site tape, which is sighted in for “at home” conditions near El. 1000 ft, and if there were a big enough difference between FP and BH site tapes, I’ll just make a mental note of the difference and adjust in the field. Again, all this is assuming “it matters” a significant amount within your Max Effective Range. I wanted to check if it did make a difference and by how much.

With that said, I measured a 2.5 to 3.5 fps average difference between field points and broadheads at 20 and 70 yards. Using that info for the site tape, and with same D.A. and bow/arrow data, the site tapes only differ by 1 yd mark between 60 and 80 yds, and basically 2 yd marks beyond that. Using a higher elevation, say El. 6000 ft for my hunting area, the added drag of the broadhead compared to the field point is offset by the atmospherics at the higher elevation. The resulting site tapes are virtually identical out to 60 yards. For a more extreme case, say El. 10,000 ft, even with the broadhead, the ballistics show it could be slightly “hot” compared to the field point at home. Obviously this is just was the ballistics show. At the end of the day, it seems very worthwhile to verify your POI once you arrive at the hunting area.

 

[Marble]

This is exactly what I was after. Actual data or experience in drop differences at 80yd from significant DA change. Thank you for sharing.

What he reported is my exact experience. If I'm shooting pins, there isn't enough there for me to mess with anything as far changing pin gaps. But when I'm shooting a sight tape either on my spot hogg or my target bow, which has an Axcel XP Pro, I will shoot those distances out to ~110 yards. It's easiest for me to check the longest distance I need to shoot, check my 20 and my 3-4 yard marks, then recalculate. The difference is generally less than 2 yards, or none at all. Using Archers advantage, I can shoot in each mark and edit my tape accordingly. I can see the calculated mark and my shot in mark.

Just to get into the weeds a little bit. The very high level archers know what their bows will do when hot, cold or wet. All three conditions will vary their desired accuracy enough to compensate. But for guys like you and me in a hunting situation, we probably dont have the skills to shoot that well. Plus the target we are trying to hit is the size of a pie plate (or larger) instead of a smaller "spot".

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