Loaded a Nosler 180gr partition over 70.0gr of
rl 19 in a 300 win mag. I have no chrony at the time but the load shoots great. Well here in texas it is 90f. In Colorado it will be 20f. What should i see as far as fps loss? The balistic program that I have shows elevation drops on the conservitive side when I have good chrony data. Any input would be helpfull.
Sorry I put this in the wrong fourm.
I'm new ok..

One of my buddies has a 264mag. He has a scope to compensate for the different ranges. It is a tack driver all the way out to 700 yds. He shot it yesterday, it was in the 90's. The bullet hit 7 in high at 500yds.All his calculations are based on a 40 deg. temp..I suspect you will see a considerable drop.

Unless you are going to the Eastern part of Colorado you are going to be at a much higher elevation (thinner air, less drag) than you would have in most parts of Texas...and it is normally far less humid (dryer air less drag) than it is in Texas.

Did you factor in those two variables into your ballistic program?

A 50 degree temperature change in the same geographical location is not going to have the same effect ballistically as a 50 degree change in temperature coupled with similar large changes in both elevation and relative humidity.

The increase in elevation and the decrease in humidity could actually have the exact opposite effect you are expecting from the change to colder more dense air. Those two variables, depending on how much they are, could actually cancel out the temperature difference.

I have been going from the Heat of TX to the cold of CO over the last 25+ years. I always check my rifle zero I have never had to change it. My programs show a change of maybe 1-2 " at 400-500 yds. Slightly offset by the elevation change. What you will find is a 10deg up or down angle will have that much change and by the time you get to 20 degs you are talking 4-8".

I would not worry about the temp change it is small compared to the angle of the shot.

I`ve crono`ed loads here in Michigan in temps from ~5-10F (any colder I stay off the range) to 95+ F and can say the only way to tell how the temp will affect your vel is to crono it. The change of components sometimes makes almost as much difference as the temp in velocity. Change the powder lot and you might see a 50-75fps drop. The others are also right, there are other factors to consider beside temp.

I remember seeing a figure somewhere of 1.5 fps change per degree of temp change as a rule of thumb. This is close to what I`ve seen depending on the powder, but I would guess a drop of about 100fps with a 70F change. (90F-20F)

I was always taught that whenever you travel long distances with a scoped rifle you should always re-check your zero whether the atmospherics have changed or not just to make sure nothing has “moved†on you.

The shooting distances where atmospherics start to become a factor to be seriously considered are normally well beyond normal hunting distances anyway.

And look on the bright side...if you don’t bag something you will have the perfect excuse!