[Lycoming]

What weather condtions produce the better results at the range? Forget about wind. We all know that no wind days are best. But, for instance can one expect to see better shot grouping on forty degree, low humidity days? Or, would higher humidity and warmer temperatures be better? How will these conditions, temp. and humidity effect bullet flight characteristics?

 

[Jeffvn]

Best weather at least for me in Houston is going to be little to no wind, cloudy to stomp on the mirage, steady temperatures in the mid to high 70s. Cooler temps tends to reduce veolcities by inhibiting powder burn (the opposite of high temps increases pressure and causes velocities to go up).

I prefer some wind to dead calm, as there is never a true dead calm and I at least want to know what direction its coming from.

JeffVN

 

[mele]

Yes, cooler temps cause not only slower velocities, but thincker air which adds to the slowed initial velocies by slowing the bullets faster, causing even a big drop in ballistics. BUT, if you are going for tight groups, cold air tends to be the best because it is more stable (especially if you are talking longer distances where unstable air has a longer time to affect bullet travel). Overcast is indeed better for mirage purposes.

MEL

 

[spade]

Temperature affects the firer, ammunition, and density of the air. When ammunition sits in direct sunlight, the bum rate of powder is increased, resulting in greater muzzle velocity and higher impact. The greatest effect is on the density of the air. As the temperature rises, the air density is lowered. Since there is leas resistance, velocity increases and once again the point of impact rises. This is in relation to the temperature at which the rifle was zeroed, If you zero your rifle at 50 degrees and you're now firing at 90 degrees, the point of impact rises considerably. How high it rises is best determined by recording past shots fired. The general role, however, is that when the rifle is zeroed, a 20-degree increase in temperature will raise the point of impact by one minute; conversely, a 20-degree decrease will drop the point of impact by one minute.

Humidity varies along with the altitude and temperature. You can always encounter problems if drastic humidity changes occur in the area of the shot. Remember, if humidity goes up, impact goes down; if humidity goes down, impact goes up. As a rule of thumb, a 20-percent change will equal about one minute, affecting the point of impact.

At least thats what my uncle always told me. He was a USMC Scout Sniper during Vietnam.

 

[Shoe]

Spade:

Interesting to hear the practical side of it. Only thing I could think of was the theoretical stuff from my fluid mechanics courses relating drag coefficients to air properties that are functions of temperature. Very much theoretical, but would give you the right trends. Nice to see a quantitative measure of them though...

 

[mele]

Yep, all of that is correct and known, but Lycoming was specifically asking what weather would help contribute to better grouping, not better (flatter) ballistics. And nice thick & stable air would be best.

MEL

 

[Lycoming]

Weather

Yeah. All of the info is helpful. It all makes sense too. Just what I was looking for. In depth responses to my question. I appreciate it.

 

[Shoe]

Yah, Mel's right. Stable air is the best, thick or not. Unfortunately, hot air tends to have very unstable winds, updrafts, and other convection currents that aren't very conducive to stability.

Ideally, the best air is uniform in properties all the way from muzzle to target. I suppose that taken to the extreme, shooting in a vacuum would be best, but that's not an easy thing to do.

 

[anomalous_result]

shooting in a vacuum raises an interesting question, for me at least - is there enough air in the cartridge to enable all the powder to burn, or is there some inlet of air somewhere? from gcse chemistry i'd hazard a guess that there wouldn't be nearly enough, but i don't know how much of the cartridge is empty space. ideal conditions then would be shooting into a vacuum, say throguh a rubber sleeve type thing, could manufacturers do this and then quote the moa from that?

 

[AKvsAR]

A little late in reply, but since you can fire rounds under water, you can fire in a vacuum. Just my .02 cents

 

[madgunsmith]

This is not very scientific, but the best groups are shot in comfortable weather.

I just can't shoot very well in the cold.

I think that 70 degrees is the best shooting weather. Although one time I was in South Dakota and it was about 85 degrees. I was at a friend's ranch and he had about a million prairie dogs. I must have shot several hundred of the little beggars. I think I might have even fried a 6.5x55mm barrel.

But nice warm weather, lots of targets and lots of ammo. It just doesn't get any better than that.

Mad

 

[spade]

A little late in reply, but since you can fire rounds under water, you can fire in a vacuum. Just my .02 cents

actually, i would think no... because when you bring a weapon underwater i little bubble of air is stuck in the barrel generally... and says there to help the ignition process. In a vacume ALL air would be sucked out of the aera... even the gun. So not enough air would be availiable to show a true ignition.

I think this is how it works, but i culd very well be wrong.

 

[muzzleblast]

Try to fire your weapon underwater and you will have a very unique customized rifle when it blows up