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Author Topic: Spring-piston rifles -- changes in latitudes and altitudes  (Read 3487 times))

Offline gokidd

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Spring-piston rifles -- changes in latitudes and altitudes
« on: April 20, 2018, 05:14:31 PM »
For those who have traveled far and wide, high and low with a sub-12 fpe spring piston rifle, a couple of questions.

I'm traveling to a meet that's staged about 4000 feet higher than my regular altitude.
How do you plan for this change in power?

Do you take a chronograph with you and remeasure muzzle velocity at that new location?
If so, do you then use an elevation turret with generic "click" markings instead of a custom (like ScopeKnob) turret label with exact distances?
IE: Just use a generic click scale and an updated DOPE sheet for the new power setting?

Many thanks,
Bob


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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #1 on: April 23, 2018, 02:04:20 PM »
Do many of you simply use the standard markings on the OEM turrets all the time?
Bob
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Offline dan_house

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #2 on: April 23, 2018, 02:20:42 PM »
you're going to the Nevada match at Battle Mountain? they should have a chrony there, at least they did when I went in'16

Im using PP-Calc, so I get a new chrony number, take some meausrememnts at 3 distances 10, 45,55 yards and plug that into the program and itll calculate the new dope.

But Im worrried about the thnner air doing weird things to my springer,,,,,,   If I get to go
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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #3 on: April 23, 2018, 02:26:03 PM »
you're going to the Nevada match at Battle Mountain? they should have a chrony there, at least they did when I went in'16

Im using PP-Calc, so I get a new chrony number, take some meausrememnts at 3 distances 10, 45,55 yards and plug that into the program and itll calculate the new dope.

But Im worrried about the thnner air doing weird things to my springer,,,,,,   If I get to go

Exactly, Dan.
So you are using the standard turret that came with your scope?
In other words, your DOPE sheet uses measurements like 1:6 and 2:3, etc? In MOA or MIL or whatever.
Bob
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Offline Scotchmo

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #4 on: April 23, 2018, 02:31:57 PM »
Applies to any piston gun, not just 12fpe:

In my opinion, a well tuned piston gun has a small amount of piston bounce. Maybe 20% maximum. That will allow it to function fairly consistently from sea level up to about 2000' or so elevation. It gives up a little efficiency, but avoids piston slam. If you want to operate over a greater variation in atmospheric pressures, you are better off with a soft tuned, full stroke gun. If you are tuned optimally for sea level operation, but are shooting at 4000', you might have some piston slam. Power will be reduced and you might be damaging the gun's power plant. You can still shoot it (I wouldn't), but be prepared to deal with the consequences.

As the air thins, the BC increases. If you are lucky, the BC increase will compensate for the velocity loss, and your dope won't change much. When in doubt, best to have a backup plan (PCP). Shoot your piston gun over the crony after you get there and then decide.
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Offline dan_house

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #5 on: April 23, 2018, 02:37:24 PM »

So you are using the standard turret that came with your scope?
In other words, your DOPE sheet uses measurements like 1:6 and 2:3, etc? In MOA or MIL or whatever.
Bob
I dont click. YEs factory turret. I hand write my doep sheet after getting match specific numbers and drop
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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #6 on: April 27, 2018, 03:10:17 PM »
Applies to any piston gun, not just 12fpe ...

Great info, Scott.
I thank you very much.
Bob
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Offline Motorhead

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #7 on: April 27, 2018, 04:51:02 PM »
Bob,
watching past National spring gun champs like Keven Yee, he has his base line dope and then once on site & during practice he shoots different distances and makes NOTES of differences of hold ACTUALLY REQUIRED.  Done at 10-15-25-35-45-55 yards one can fudge the distances in between easy enough. 
As the day heats up or cools down ( Air density changes ) and you start seeing a trend in POI shifting, by having BASE LINE and ACTUAL location corrections required get a closer idea on what the shift will be across all ranges.

Frankly springers change so much in this regard that doing actual "Johnny On The Spot" tests at the 6 five yard gaps may be a more productive practice for you ???

JMO tho,
Scott

 
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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #8 on: April 27, 2018, 06:40:52 PM »
Frankly springers change so much in this regard that doing actual "Johnny On The Spot" tests at the 6 five yard gaps may be a more productive practice for you ???

Yep, I'm thinking I will take a chronograph with me and a generic turret label numbered in clicks.
Shoot the distances I need for Pellet Path Calculator and then then write up DOPE for the specific locale.
Many thanks,
B
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Offline dan_house

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #9 on: April 30, 2018, 08:14:56 PM »
Pellet Path Calculator

yep, thats good stuff to use.
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Offline Kerndtc

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #10 on: June 05, 2018, 04:11:00 PM »
Don't you love when. You are worried about prep for shooting a Piston in a higher altitude and when you get there almost nothing changed??

I was worried as well, but luckily my numbers were the same there as they were at home. I couldn't believe it.

I had about 30 minutes last night to shoot my 97 and the zero was right, close to 5/8" couldn't have been the right to left wind we were experiencing lol. Other than that everything else was on and accurate.

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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #11 on: June 05, 2018, 05:40:15 PM »
Don't you love when. You are worried about prep for shooting a Piston in a higher altitude and when you get there almost nothing changed??

I was worried as well, but luckily my numbers were the same there as they were at home. I couldn't believe it.

I had about 30 minutes last night to shoot my 97 and the zero was right, close to 5/8" couldn't have been the right to left wind we were experiencing lol. Other than that everything else was on and accurate.

Cam, I was just thinking I should come back here and report, too, since I raised the question.
I think the elevation in Horse Canyon was right about 5000 feet above sea level.
My HW97 shot 790 fps on Lonnie's Chrony there. At home, my gun shoots 780 fps.
So pretty much the same performance at 200 feet above sea level as 5000 feet when allowing for differences in the two Chrony setups. I shot the same DOPE.
Go figure. Scott Hull knows too much about springers.  ;)  ;)
Bob
« Last Edit: June 11, 2018, 05:00:15 PM by gokidd »
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Offline Motorhead

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #12 on: June 06, 2018, 02:01:38 AM »
Don't you love when. You are worried about prep for shooting a Piston in a higher altitude and when you get there almost nothing changed??

I was worried as well, but luckily my numbers were the same there as they were at home. I couldn't believe it.

I had about 30 minutes last night to shoot my 97 and the zero was right, close to 5/8" couldn't have been the right to left wind we were experiencing lol. Other than that everything else was on and accurate.

Cam, I was just thinking I should come back here and report, too, since I raised the question.
I think the elevation in Horse Canyon was right about 5000 feet above sea level.
My HW97 shot 790 fps on Lonnie's Chrony there. At home, my gun shoots 770 fps.
So pretty much the same performance at 200 feet above sea level as 5000 feet when allowing for differences in the two Chrony setups. I shot the same DOPE.
Go figure. Scott Hull knows too much about springers.  ;)  ;)
Bob


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Offline JKC

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #13 on: June 06, 2018, 10:07:37 AM »
This is insane.

Do you springer guys use a crank to start your vehicles?  ;D ;D

Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #14 on: June 06, 2018, 11:32:23 AM »
This is insane.

Do you springer guys use a crank to start your vehicles?  ;D ;D

What is this "vehicle" of which you speak, sir?
We use our shoes and keep a spring in our step.
HAAAAAAA!

Jack, yer a Dickens.
B
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Offline Kerndtc

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #15 on: June 06, 2018, 12:47:53 PM »
This is insane.

Do you springer guys use a crank to start your vehicles?  ;D ;D

Haha. I just keep my 5 speed on a hill so I don't have to connect the crank start linkage!

I miss my PCP... it's like a drug or something.
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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #16 on: June 06, 2018, 12:53:49 PM »
I had a Ball Point Pen in my pocket all weekend ... it has a spring and seemed to work just fine
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Offline Scotchmo

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #17 on: June 06, 2018, 06:52:12 PM »
Don't you love when. You are worried about prep for shooting a Piston in a higher altitude and when you get there almost nothing changed??

I was worried as well, but luckily my numbers were the same there as they were at home. I couldn't believe it.

I had about 30 minutes last night to shoot my 97 and the zero was right, close to 5/8" couldn't have been the right to left wind we were experiencing lol. Other than that everything else was on and accurate.

Cam, I was just thinking I should come back here and report, too, since I raised the question.
I think the elevation in Horse Canyon was right about 5000 feet above sea level.
My HW97 shot 790 fps on Lonnie's Chrony there. At home, my gun shoots 770 fps.
So pretty much the same performance at 200 feet above sea level as 5000 feet when allowing for differences in the two Chrony setups. I shot the same DOPE.
Go figure. Scott Hull knows too much about springers.  ;)  ;)
Bob


5800 at the match site ...

If a piston gun's velocity increases or stays the same at altitude, then you likely have some piston bounce at sea level. A little bounce is not a bad thing. A gun with 50cc swept volume and only 12fpe is a "soft" tune. There is a lot of extra air volume to spare. I believe that the HW97 is 43cc swept volume. My QB58 is about 37cc swept volume (originally 33cc), so not much to spare. The more extra air volume, the greater the tolerance for variation in ambient pressure.

Ideally, you would have just enough air volume, just enough piston mass, and just enough spring energy for the pellet used and available air pressure. That will give the shortest lock time with the least total recoil. But it's good to have some "cushion". Bob, you obviously had sufficient cushion for even 5800 ft elevation. My QB58 has less cushion, so I set my limit at 3000ft. In the UK, they don't have to worry about 5000ft elevations, so short-stroking them is popular for 12fpe FT piston guns.
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Offline gokidd

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Re: Spring-piston rifles -- changes in latitudes and altitudes
« Reply #18 on: June 06, 2018, 07:41:29 PM »
GREAT perspective and data, Scott.
Thanks for your help, bud.
Bob
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