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Spring-piston rifles -- changes in latitudes and altitudes

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gokidd:
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

gokidd:
Do many of you simply use the standard markings on the OEM turrets all the time?
Bob

dan_house:
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

gokidd:

--- Quote from: dan_house 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

--- End quote ---

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

Scotchmo:
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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