Effect of Weather Conditions and Elevation on .22LR?

Discussion in 'Rimfire and Airguns' started by Josh Smith, Jul 25, 2010.

  1. Josh Smith

    Josh Smith Member

    Jul 24, 2010

    I sighted in my rifle (Savage Mk II .22 BTVS) in dead calm conditions. I zeroed it in at 50 yards, and with a few clicks' adjustment in elevation only, I was making very close to 1moa hits with junk ammo at 100yds.

    This was shooting a couple degrees UP, laying prone.

    Last night, it stormed hard. The town flooded out, and I was fighting flooding conditions here in the country.

    Today, it is much, much less humid. When I sighted it in before, we were anywhere from 88% to 99% humidity, dead still.

    Today, as I said, less humid (it's all in the creek!) and I have an eight to 10mph wind blowing.

    I decided to shoot a few things from my alternate perch, which is about three feet higher than my usual shooting spot. It put me dead inline, or slightly above, my targets at 50 yards.

    It looks like I'm hitting about 1/2" high.

    Now, I know the POI raises when you shoot uphill, but by this much at 50yds?

    I need less variables. I need to shoot from the same spot from which I sighted, but unfortunately I cannot post new targets since the humidity is now in the creek, which I must cross in order to get to even my 50 yard target holder.

    So, in short, here are the new variables:

    1. Sighted in at 50yds in dead still conditions. It is now 8-10mph from the east.

    2. Changed from shooting slightly upwards to straight or slightly downwards, which is less comfortable for me.

    3. Humidity is much less than previously.

    Would the above factors combine to give me a higher POI with the same ammo? As I said, isolating the factors is kinda' out of the question right now.

    Thank you,

    [​IMG] [​IMG]
  2. Kevin Thomas

    Kevin Thomas Well-Known Member

    Feb 16, 2009

    Lotta questions here, and a bit overwhelming to try to answer all of them in one statement. The answer is yes, it'll change. Problem is, and of the variables you mentioned here will cause those changes. If it rained, then that means the barometric pressure fell at some point, which will cause your rounds to shoot flatter than on clear sunny days of higher BP. Humidity has it's effects too. Very humid air is lighter than dry air, and will cause the same effect as low BP, a flatter trajectory. You mention uphill and down hill angles; same thing. So you can see, when you start adding all these things together there's a lot of interactions going on, some of which will add to or cancel out others. You can play around with any of the ballistic programs out there and see what some of these things will do when you change them, at least as a starting point. If you want to ask your questions one at a time, you'll probably get more concise answers here. Trust me, it's easier that way.

    Kevin Thomas
    Lapua USA
  3. FAL Shot

    FAL Shot Well-Known Member

    Oct 9, 2010
    Was there heat mirage visible in your scope? If you sight in a rifle early in the morning around here, when you see boiling heat mirage through your scope later in the day, you will be hitting high. It can be a lot more rise than 1/2" rise at 50 yards. It's the heat near the ground, not higher up at standing head level I'm talking about. You can have considerable heat mirage near the ground even on a windy day when you aren't bothered with it as much standing up. It's the visual image floating above actual location caused by refraction of light rather than altitude density change caused by higher temp that makes the biggest difference.