seems to shoot lower in the cold

[OLD CHIEF]

While working up a load for a new bullet this winter it has looked like the colder it is the lower my gun will shoot. not a lot for small temperature changes but when it went from the high 60's one day to the mid 40's the next it seemed to shoot at least an inch or more lower on the100 yard targets. Is temperature that much of a factor or did I do something different in the cold? And if it is a factor how do you work on your sights and loads in the winter and then shoot in the summer when it is at least 40 degrees warmer? I know that you can find black powder ballistic tables for bullet weight, wind, etc. is there one for temperature?

Bill Hicks

[Macallan]

Old Chief,
You are not doing anything incorrectly. Temperature will affect muzzle velocity. The higher the air temperature, the greater the pressure inside your case. When the external temperature decreases, internal ballistics pressure decreases thus your bullet has a slower muzzle velocity and will strike the target lower.

The next time you attend a match, watch other shooters' target strikes throughout the day. As the temperature increases during the day, you may notice bullets tend to hit higher on the target (especially at long range) unless shooters make sight setting adjustments.

During practice, I keep track of temperature and sight settings throughout the day. As the temps increase or decrease, I can automatically make adjustments.

Every shooter, rifle and load will see different results. For me, I have found I need to make roughly 1 MOA adjustment for every 10 degrees of temperature change. Keep in mind that changes in humidity, wind, position of the sun etc. are affecting your external ballistics or sight picture through out the day so it isn't just temperature you have to worry about. You may not notice any great changes in short to mid ranges but you will definitly notice a difference when you go beyond 600 yards. You will notice this in the summer too when you begin shooting in the morning at 70 degrees and then end your day when the temps are 90 to 100 degrees.

The only way to figure out your exact sight settings is to shoot the same load at different temps and keep track of your sight settings for future reference.

I hope this helps.

[klw]

The local library had a copy of the 1935 Naval Academy textbook. Contained an interesting section on cold gun errors, i.e. cold guns shoot low. I went out one winter and sighted a 22 target pistol in at 25 yards. Ransom rest I think. Repeated the study several times later in the year as the temperature rose. Sure enough a cold gun shoots low.

Also tried the same thing but in the summer in the bright gun. The more sunlight on the ammunition the warmer it was and the higher the point of impact.

[Harry Eales.]

In addition to the above 'posts'

Air is denser at low temperatures, therefore, there is slightly more drag on the bullet and thus a lower trajectory.

A change in altitude will also cause a change in the point of impact. At high altitude the air is also less dence and even if the temperature is the same as at a lower altitude the POI will differ.

Life gets confusing at times, especially if you shoot Black Powder.

Harry