Temperature wind, and zero

[mshootnit]

Help me with this scenario.
243 rifle 90 gr. ammo H414 powder, this rifle was zeroed by me exactly 2" high at 100 yds. The weather was 95 degrees with a 15-20 mph tailwind.
Question is: Now where would this rifle hit at 100 yds and beyond... into a 15 mph headwind at a temperature of 35°F.

 

[z7]

The head wind/tail wind should not matter, ignore it

I can’t say how the temp change will influence pressure and harmonics

 

[pintler]

Not enough data.

You can plug the BC for whatever bullet you're using, muzzle velocity, etc into one of the ballistics programs and it will give you corrections for the barometric pressure change (resulting from the temp drop).

The open question is how such a temp drop affects your particular powder/primer/etc. AFAIK, you have to determine that yourself experimentally.

Note that what matters is the temp of the powder at ignition, which may be different from ambient temp if you've fired enough to warm the gun up, or if you've carried the ammo in a warm pocket, or just brought it outside from a heated building, of let the sun shine on it...

 

[Slamfire]

If this was a rimfire the bullet will drop. But, 22LR's have all the ballistics of spit balls, which is why shooting the things accurately takes great wind reading abilities. I have shot matches in 40ish weather, I can recall two matches in the snow, and what I can say, for a centerfire rifle, in the cold, your response to cold will have a greater effect on point of impact than cold will have on the gun. In cold weather I dress in layers. Because my bulk diameter has changed, my stock weld is different. Shooting a rifle standing in the cold, you either strip down and freeze, or you try to adjust to the rifle way the heck off the shoulder. In the cold, my fingers are cold, I take my gloves off on the shooting hand so those fingers hurt. My eyes dry out if the wind is moving, all things considered, it is hard to shoot accurately when dressed like a polar bear with stiff cold fingers and blurry eyes.

Don't worry about bullet drop. Worry about keeping warm.

 

[mshootnit]

so you could keep the shells in a warm pocket, and pretty much have the same zero even in 60 degree coldee weather?
Also, a difference in wind of basically +40 mph, nothing to worry about for a 8" target out to 300 yd?

 

[243winxb]

The tailwind pushed bullets down, creating a false zero.

The headwind will make the bullet impact higher.

35F produces less velocity then 95F

My 90 gr Berger doesnt like the cold in a 1-10 twist barrel.

Now where would this rifle hit at 100 yds and beyond... into a 15 mph headwind at a temperature of 35°F.

Higher then the orginal 2" high zero.

 

[pintler]

so you could keep the shells in a warm pocket, and pretty much have the same zero even in 60 degree coldee weather?
Also, a difference in wind of basically +40 mph, nothing to worry about for a 8" target out to 300 yd?

1)Temperature of the powder affects powder burn rate, and thus pressure, and thus muzzle velocity.
2)Air temperature doesn't directly affect trajectory, but it is usually associated with higher barometric pressure (because, all other things being equal, cooler air is denser air). Denser air affects trajectory.

A 40 MPH wind will have a huge effect if it's coming from the right or left. It will have less effect coming from straight ahead or behind. If it's coming from 10 degrees off the bullet path, it will have more effect than from zero degrees. If it's blowing 20 MPH it's probably swirling around a little.

A precise answer to your questions depends on your exact muzzle velocity, the exact ballistic coefficient for your bullet, your twist rate, ... ad nauseam.

You can get free ballistic apps for smartphones, or here is an online one:

https://www.hornady.com/team-hornady/ballistic-calculators/#!/standard

Select the '4DOF' calculator and you can plug in your actual numbers and tweak things to see what the effects are likely to be. Other than the ammo temp issues. I doubt those matter much inside of 300 yards, but vary the muzzle velocity some and see what happens.

 

[ontarget]

I don't think you will see much if any change at 100 yds. Most shooters are not consistent enough to even see a change at 300 yds under the conditions you are asking about.

 

[Llama Bob]

You're not going to see a meaningful difference at 300y.

 

[Varminterror]

The temperature may matter at longer ranges, not significantly so at 100yrds and under, or even 300yrds and under. H414 is a double base powder and can be a bit more temperature sensitive, so a guy really should take a few shots to see how much his velocity is affected, however,

The wind, however, from tail to head, means nothing of meaningful consequence. Changing from a 20mph tail to a 15mph headwind is equivalent to a 51fps ES in muzzle velocity - not great, but insignificant until you're shooting long ranges where 50fps ES would present itself as vertical dispersion.

 

[denton]

The result is unpredictable.

The shock wave of the firing pin drop and the ignition of the powder travels down the barrel faster than the bullet, causing the muzzle to vibrate. This is called barrel whip. Where in that arc the bullet exits the muzzle influences point of impact. It depends on barrel transit time, and with most powders 60 F will make a significant difference. You may find your POI has shifted up, left, right, down, or not at all (if you're very lucky).

Check your sight-in and muzzle velocity at 35 F and adjust accordingly.

A lot of the literature says that it's the temperature of the powder that matters. It's not. Or at least not very much.

Cold steel and brass rob energy out of the propellant gas. What matters is mostly the temperature of your barrel, close to the receiver and the temperature of the brass and lead. In the experiment I did, barrel temperature was about 3X as important as ammunition temperature.

 

[MCMXI]

In addition to many of the issues already discussed, a bullet's stability in flight (gyroscopic and dynamic) can be significantly affected by a drop in air temperature. A load that is accurate and precise at 90F might be terrible at 30F particularly if bullet stability is marginal at 90F.

 

[GAF]

I check the zero on all of the guns I plan on taking to deer camp in as close to the conditions I will be hunting in.

 

[Art Eatman]

To 300 yards or thereabouts, the only detrimental effect in a hunting situation would be crosswind. Not enough effect from head- or tail-winds to worry about. And in a bunch of years of hunting, temperature has never made any difference, from warm to cold.

 

[jmr40]

You'll see 1/2-2 fps slower bullet speed for each degree temps drops. At really long ranges it could make some difference. You'll just have to shoot your ammo, in your gun over a chronograph at 95 and 35 degrees and see how much it changes.