Higher velocity in cold or warm weather?

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Mikie

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I was reading some chrono'd rounds at the Tactical Firearms Website and found something interesting. The same factory load, Remington 165 gr Golden Sabre, through the same gun, a Sig P229 was clocked at 952fps in July and 1022fps in January. Does anyone know will the same cartridge(bullet, weight, powder charge, case) in the same gun achieve higher velocity in cold or warm weather and why"

Thanks

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One would think that in the winter time when metal has not expanded to its natural state that the velocity would be slower since the barrel is smaller in diameter causing more friction for the bullet. In the summer when the barrel has expanded the bullet goes throug easier. Not to mention that air is denser at lower temps.

Just my opinion. I could be wrong. wouldnt be the 1st time.

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TIM : )
 
The answer can be found in this anecdote:
-----------------------------------------
Q. Why can Robin Hood see much better at
night than during the day, in the woods?

A. Because, during the day, trees obstruct
his vision, and at night, he does not see
these trees.
------------------------------------------
On the serious note, call Weather Channel
for answers on weather/temperature and
bullet velocity correlation.
 
Oris - huh?

JERKY - not a bad theory, but I think that the barrel doesn't contract or expand enough to cause what you describe.

There are two reasons for changes in velocity at different temperatures. In cold weather, the air is denser and the bullet's velocity is slowed since it has to plow through, essentially, more air. But another reason is that smokeless powder will create less pressure at lower temperatures, less pressure = lower velocity. In the test Mikie related, the only important one is the powder/pressure one since it was a handgun and was probably measured close to the muzzle instead of 100 yds down range. Several things that could cause the reverse of what is expected are: were the tests conducted indoors or out? was the gun hot or cold when the tests were made? Also a 70 fps range isn't all that unusal even from the same lot of cartridges, so we may be wasting our time trying to figure out a non-puzzle.

Oh, and I just remembered one other thing - where were the tests conducted? Arizona? Yukon? Or if say, Australia, then that would explain it.

[This message has been edited by Mal H (edited November 21, 1999).]
 
Historically most powders are more volitile as temperatures rise just like most chemical reactions. Old cordite was notoriously bad and that is why the British cordite rounds were loaded at 40,000 or less so their use in the tropics didn't blow up the Queens firearms. We now have special powders (such as Extreme from Hodgdons) that is engineered to be rather immune to increases in pressure as the temperature rises. Seems strange to me that it happened as you reported, but I have seen most everything over the last 50 years of reloading. I had a load last year that gave me the best velocity with the starting load and then decreased with each heavier load. Guess it had something to do with the fact that they started out highly compressed and more powder didn't really help? A buddy in Montana will not use BLC-2 saying that it loses too much velocity when the ice starts forming up there in Montana. Have fun, Jim
 
As Mal H points out, air in denser when cold. If objects are dropped from a fixed height, it will be slightly SLOWER in the cold, so changes in air friction in different temperature wouldn't explain it.

What I think is going on it that the cold and subsequently increased oxygen concentration allows for a denser, more complete combustion. I worked with a gear-head anaesthesiologist who use to squirt nitro into his engine. Over a surgical case, he explained to me that the reaction the occurs in endothermic (sucks up heat), allowing for a cooler, more powerful, denser explosion and increase in horsepower. Car gurus can correct me if I understood incorrectly, but this guy was a Harvard professor and not a bull****ter.
 
Sorry Teppo, unlike humans, powder doesn't need atmospheric oxygen to burn. It has all it needs built right in.
 
Constant ammo testing has proven to me that the temperature affect will not be known until actual testing occurs.
I've had loads go in both directions; faster when hot, faster when cold. I try to test my ammo over a two-year period to confirm the initial testing.
Some loads go faster in warm air, some go slower.

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"All my ammo is factory ammo"
 
The Lot of the powder, bullet and primer have more effect than the temparture. That being said, temparture effects have been quantified for at least military ammunition. So once you have achieve a baseline at what ever temperature it is possible to predict what the effect for a decrease or increase in temperture will have on the projectiles MV. The biggest factor that effects the MV is the powder temp, for some the reasons listed above. If you look in every TFT (tabular firing table) you will see the effect for powder temp are quite large while the effect for changes in atmospheric temperature are small.
 
Hmmm, maybe in the winter the gun was cold and the inside diameter of the barrel was smaller, so there was more resistance to the bullet, higher pressures, and consequently higher velocity? Of course, even if this was the case, it would only hold true for the first shot. Yes, the bullet would've shrunk slightly too, but steel vs. lead have different characteristics and different distortion from temperature changes. I dunno, just a guess. -Kframe

BTW, Jerky thought of this first. I just missed it while scrolling thru. Oops.
Not trying to steal any thunder. -K

[This message has been edited by Kframe (edited November 23, 1999).]
 
Kframe, I think you are close to uncovering
this mystery. I have the same understanding
as you. I.D. of the bore shrinks under the
influence of temperature, which causes
more gas pressure to be generated to push bullet thru (time delay). You are also right that it would be the case for the first shot, may second too...
 
Ok, you forced my hand. Gun barrels don't expand or contract enough to account for large differences in bullet velocity. The coefficient of expansion for the average gun steel is around 11 microns/meter/deg C. An assumption of the start temperature of the barrel on the two days in winter and summer has to be made and I assume the temp difference is 30 deg C. For that temp differential, the barrel ID will contract around .00013" for the first shot in a barrel that has reached the ambient temperature. Most bullets aren't even manufactured with that kind of tolerance. If any of you think that that small a change is going to make a big change in bullet velocity, then you have to explain why a gun/bullet combination can achieve single digit standard deviations in velocity even though the barrel can be 60 deg C hotter at the end of the test.

We still need more info on the test environment itself before going any further.
 
Same loads (exact load, stored on shelf), two years apart, fired in warm (80F) and cold (10F) outside temp.

Same loads (exact load, stored on shelf), two years apart, fired after being stored 24 hours in warm (85F) and cold (-10F) temps.

The tested loads performed the same two years apart; some go faster when cold, some go slower. I believe the gunpowder used is the biggest factor in temperature-based velocity swings.

Any loader with enough different powders and a chronograph can test this themself.

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"All my ammo is factory ammo"
 
If the ammo was from the same box, then I couldn't tell you... but performance can vary differently from lot-to-lot.

That was probably already said, but I didn't have time to read each one.

Cheers,
Ben

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AOL IM: BenK911
ICQ # 53788523
"Gun Control Is Being Able To Hit Your Target"
 
A exact batch of 9mm that I loaded and shot when it was 76 deg. had a chrono of 1196 fps, again exact same load fired at 38 deg. averaged 1170 fps.........I asked about it on GT and everyone said it was the powder.

However, the best was a guy (Military Type) that said SNIPERS take the temperature into account on their very long shots to make a slight adjustment in their sights....I like that.
 
Temperature and air density make a lot of difference and temperature is not the only thing that causes changes in air density.
Powder generally burns faster as temperature rises. This may or may not increase velocity.
Condition of the weapon as well as barrel length also can make a difference.

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Better days to be,

Ed
 
Artillerymen have been taking these factors into account since prior to WW I. ALthough you have certain quantifiable items. With manufacturing tolerances no 2 rounds with matching lots of power, primer and projo (add brass for fixed ammo) will have the exact same MV. They may be extremely close, so close that the primative devices used by most civilians could not detect the diffrence. The only way to truelly show the diffrence, is to bolt that weapon into a fixed platform with zero movement, fire the rounds, if the 2 rounds don't go into the exact same hole( of course no wind effect), the MV was different. According to the artillery standards if 2 rounds are with 3 MPS of the average for that lot, than they are are considered with in the norms and are not rejected for calibration purposes. Now cold tubes do generally have a different MV than a hot tube, but an extremely small one, a greater difference will occur because of that clean tube going to a fouled tube after the first round. As I have previously stated if you look into a TFT you can see the effects of powder temp are normally far greater than the effects of air pressure or temparture.
 
If memory serves, a TFT is a tabular firing table which is a book that essentially covers the effects that variables have on the distance and direction that a fired projectile will go.

And drift is a function of time of flight.

And Snow Hall is probably still there.

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Better days to be,

Ed
 
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