Weather stuff and fps

[splitbeing]

Shooting a gun that got 845fps in FL and gets 755fps in PA.  I have suspected my chrony, but a new one arrived and gets the same.  So I am thinking about weather, pressure, elevation differences.

My numbers are often lower than anticipated with a few guns. Again, suspected my chrony but now am wondering about weather.

I'm happy with fps in the 700s range. My concern is my chronys being off and my curiosity is weather impact.

[avator]

Hmmm... I would think that 100 fps would be a lofty difference to blame on climate/weather.

[ranchibi]

Like Bill said above....that's too large of a spread for weather/humidity. I shoot at sea level and when I shoot @ a friends place @ 4400 ft elevation, my FPS difference is about 20 FPS. Large discrepancy in humidity also.

[Madd Hatter]

Shooting a gun that got 845fps in FL and gets 755fps in PA.  I have suspected my chrony, but a new one arrived and gets the same.  So I am thinking about weather, pressure, elevation differences.

My numbers are often lower than anticipated with a few guns. Again, suspected my chrony but now am wondering about weather.

I'm happy with fps in the 700s range. My concern is my chronys being off and my curiosity is weather impact.

Are you talking about a Springer, multi pump, CO2, or a PCP? All are affected in different ways by elevation, Temp,etc.

[splitbeing]

Springer.

Yeah, I thought 100 to be alot too.

I suspected my chrony. Received a new one and got the same readings.  Granted, it's two of the same chrony. Maybe it's the basement light. I wonder if outside I'd see different readings.  The chrony is this

https://m.media-amazon.com/images/I/61tT1sqZKpL._SX522_.jpg

[avator]

Maybe not the issue but I did notice something with my ProChrono Digital.
If I don't pick a point to shoot at consistently I can get varied results. By that I mean shooting over the chrono high or low, side to side or at different angles.
It's not 100 fps but it's enough to make you question a regulator.

[Robert 5mm]

This is not much of a difference.
With all other factors being held equal the approximate adjustment due to altitude is 29 FPS per 1000 feet of elevation change for a spring air rifle.

Example AOA reports 800 fps for an air rifle you bought.
AOA elevation above sea level is approximately 1237 ft.
My elevation is 450 ft, or 787 ft lower.

So I should see an increase of 22.8 fps for the same pellet in the same rifle or 823 fps.

[Ronfiveo]

This is not much of a difference.
With all other factors being held equal the approximate adjustment due to altitude is 29 FPS per 1000 feet of elevation change for a spring air rifle.

Example AOA reports 800 fps for an air rifle you bought.
AOA elevation above sea level is approximately 1237 ft.
My elevation is 450 ft, or 787 ft lower.

So I should see an increase of 22.8 fps for the same pellet in the same rifle or 823 fps.

I would think the opposite should be true.
Higher elevations have a less dense atmosphere and the pellet should travel faster and farther.

I know when I played Golf in Wyo I increased my distance by 1.5 to 2 club lengths in distance.
My drives were consistently 50 or so yards longer in the thinner air in Laramie.

Ron

[avator]

Higher humidity levels will also have a certain amount of affect.
But 100 fps still seems high to me but I admit, I'm not educated in this realm.

[Robert 5mm]

Higher elevations have a less dense atmosphere and the pellet should travel faster and farther.

Less air drag at higher elevations, so the pellet retains more velocity at increased range.

But initial velocity ( energy ) is higher with the more dense air doing the pushing at lower elevation.

[Novagun]

Ok. Can we assume that the difference in mass of compressed air at altitude and the lesser air drag on the pellet evens out so we really don't have to bother about it.
Could be over simplification.

[Robert 5mm]

Ok. Can we assume that the difference in mass of compressed air at altitude and the lesser air drag on the pellet evens out so we really don't have to bother about it.
Could be over simplification.

If you are using a chronograph to compare your newly purchased air rifle from AOA ( Airguns of Arizona or other vendor ) and their reported initial end of barrel velocities then it might matter to nit picky people like me ( also an anal engineer as my wife says ).

Less air drag at higher elevations probably do not come into much effect at air rifle ranges of less than 100 yards. ( I would have to look up the air / fluid dynamics equations to get an approximated estimate of the drag coefficient )

[splitbeing]

I tried putting a light over the chrony. Same readings.

I've shot from a bench at the same bull so I think the angle is consistent.  Maybe shooting at an angle directly parallel to the base would change things a bit, but I doubt 100ish fps.

I suspect the twin chronies since adding 100ish fps to the readings of a few guns would make sense to me.

Anybody know if lighting effects these chronies?

https://m.media-amazon.com/images/I/61tT1sqZKpL._SX522_.jpg

[10Gauge]

A spring gun can lose a lot due to elevation.  I am not a scientist but i know it for a fact.  A 23-24 fpe breakbarrel at sea level, good chance it will be closer to a 19-20fpe gun in the mountains.

I might not be a scientist but i know what i know.

[splitbeing]

Difference in elevation is about 700 ft.

[Madd Hatter]

700 ft difference is not going to be 100 fps.

[splitbeing]

My hunch is that the chronograph, both of then (same model), are off in that I trust the readings in FL and adding 100fps to readings for other guns would explain a few mysteries.

I am considering buying a cheap bolt on chrony (like I used to have and could use when travelling) to test against the other two.

I suppose I could start a thread on the comparison. I have not read or seen substantive reviews of the two chronies suspected of error (both same model). The bolt on chrony would allow me to do a decent review, better than what I've seen anyway.

[splitbeing]

Bolt on chrony ordered. Will begin comparing the readings to the other chronies and the numbers I already know are good. Supposedly it arrives tomorrow. We'll see. Looking forward to providing info on the ones that have not gotten much attention if there is something worth sharing. My guess is this model deserves a warning but I don't yet know that with confidence.

[Novagun]

I am now in no doubt that weather affects spring guns. Today I shot my HW 95 for the first time in a while. Last time I shot it it was bang on target. At the time it was warm mid summer  Today was winter and cold,  well cold for us and rainy drizzly periods. The gun shot about 50 cms low at 26 metres. I can't say how much difference, the temperature and humidity had to do with it but I think the much lower temperature changed the scope sighting. I remember the same thing last year . The scope is a Nikko Sterling Mountmaster 3 to 9 x 40 AO .

[Doug Wall]

Springer.


https://m.media-amazon.com/images/I/61tT1sqZKpL._SX522_.jpg

Springers will do that. In FL, you are close to sea level. PA has a lot of hilly areas well above sea level. That means that you are trying to compress thinner air, and thus, less push to the pellet.