high humidity

[DAVEFISHING]

monsoons arrived in Phoenix . Round tail squirrels producing faster than I can get under control. I missed an easy 15yd shot, what , how? Went to my shooting stand and checked.. At 15yds 2.5 in. high , I did not check my 30 and 40yd targets. I guess I need to get a mil dot scope and preshoot ever time before I hunt?

 

[Grin_Reaver]

That or you could adjust the vertical turret adjustment on your existing scope if it is repeatable/reliable.
Another thing that may be relevant specially if you hunt for longer periods where temperature is changing is to pre-shoot and re-zero/adjust your scope turret/ hold over/under using the mildot reticle for any significant changes in temperature during the same shooting session. The extent to which you will experience changes in point of impact vs your point of aim depends on your environment and your shooting setup. The POI for spring airguns often rises or lowers counter intuitively with changing temperatures so you have to do the testing.

 

[Grin_Reaver]

I wanted to clarify why I focused on temperature instead of humidity. Changes in humidity, temperature and barometric pressure all affect the amount of drift/drag a pellet experiences in air. The measure of these atmospheric variables is called relative air density and changes in any one can cause changes in relative air density but the extent of change is different for each variable. Changes in these variables and the resultant change in down rage ballistics can be simulated by a modified ballistic coefficient for the pellet of choice.

As a rough estimate you can calculate the BC of your pellet at your local atmospheric variables and then changes each variable to see the the percentage by which BC changes. You will find that changing temperature or altitude causes relatively large % changes in BC. For example changing temperature by 20 degrees or altitude by 5000 feet will have a major impact on the BC (say 10-20% change in BC) but even changing humidity from 20% to 75% will have a much smaller effect on the BC (maybe a 1% change in BC). The % change in BC signifies the extent of change in point of impact for your pellet. 

To summarize the 2.5 inch change in point of impact at 15 yards may have more to do with temperature or shifting scope zero than with humidity.

Hope this makes sense because English is not my mother tongue.

 

[DAVEFISHING]

Temperature can be 60 f in the morning and over a hundred in the afternoon. It was around 75 f yesterday when I shot. If I remember I sited it in when it was 100f and low humidity. I have a Diana Stealth. Does temp. effect PCP as much as the springers?

 

[Arzrover]

2 1/2 inches at 15 yards is zero shift, not temperature or humidity induced poi change. Those would be fractions of an inch. Check the tightness of everything. 
Bob

 

[outdoorman]

I agree, that was my first thought. 2 1/2" at 15 yards is huge and no way would temperature or humidity cause that.

 

[DAVEFISHING]

been having issues like this for the last few months, I have posted some of my tests on here. I'm leaning towards the scope. I went out and shot it this morning, shooting back on target. Check all the hardware on gun and scope everything tight. Another thing I have the POI about 1/2 in to the right at 15yds. to hit my 43yd target. The scope is a Diana that came with the gun.