sub zero temperature affecting springers

[gurtwurz 793]

alright lads,

 

as some of you may know, me and davy had an interesting day on sunday at the southern hunters in rye near hastings. due to the weather starting at -8 we found that the trajectories of our springers had changed considerably, for example;

 

normally at 45m i shoot 4 mildots down with my .22 pro sports sr12 reticle but while it was cold i was shooting 2 mildots down, gaining an unwanted flatter trajectory, at 35m i was shooting 1mildot down so all my aimpoints were somewhat different to what i'm used to...

 

i read in an earlier thread, i think it was moley who said it, that the density of air is diminished in sub zero sonditions somewhat so it would give a faster and flatter trajectory.

 

is anybody able to elaborate on this, and also, why would a springer be affected in this manner yet pcp's behave differently, with shots dropping off after 35m?

 

cheers, wurz

[Rake aboot 4,936]

Air is denser at low temp, but I would have thought that the volume being used would remain constant, ie no extra air coming out,, just denser air.

 

Something to think about though,, It`ll bug me all day now ,,lol

[StevoSmith 147]

The only thing i can think of is the pellets themselves as air is more dence during cold conditions than warm conditions......I know that this does not effect springers like it does with CO2 or PCP rifles....with the air being more dence i would expect a drop off in pellet velocity not an increase. Gunna have a scout about on velocity in cold and warm conditions now lol

[StevoSmith 147]

Ok here is something i have found on the net....ok this chart was for a powder propelled round but prisibles are the same

 

 

 

One of the fun things about owning and using a PC or Macintosh-based computer ballistics program is the opportunity you have to see how your particular bullet / powder combination is going to perform — at least theoretically.

 

By changing the various input factors that the program uses to calculate the trajectory and speed of the bullet (i.e. bullet weight, velocity, temperature, altitude, wind conditions, etc…), you can, with the stroke of a few keys, see the effect that these factors will have on your load.

 

In this discussion I’ll be focusing on five (5) “environmental” factors that affect accuracy — Temperature, Humidity, Elevation / Barometric Pressure, Wind, and Light. Four of the five elements can be used in a ballistics program. “Light” is the only element that cannot be taken into account by the computer.

 

Keep in mind that when we shoot a Long Range match we’re going to be required to make sight adjustments throughout the match to deal with changing conditions, sometimes on a shot-by-shot basis. Knowing the effect that weather factors have on accuracy and skillfully using that information when we make those sight changes can mean the difference between missing the target completely due to a wind shift, or staying on the target for an “8”, “9”, or “10”.

 

Temperature

 

Temperature affects our shooting in several different ways:

a) It affects the trajectory of the bullet.

 

It affects the temperature of the barrel.

 

c) It affects the ammunition we use.

 

d) It affects the performance of the shooter.

 

Trajectory Considerations

 

A simple fact of physics tells us that warm air is thinner or less dense than cool air. As a result, a bullet encounters less resistance and expends less energy as it travels from the firing line to the target on a warm day than it does on a cooler day.

 

Take a look at the numbers below which were generated by my RSI Shooting Lab program:

Load Data — Caliber = .45-90 — Velocity = 1,300 feet per second — Distance = 1,000 yards — Ballistic Coefficient = .400

 

Air Temperature In Degrees

40 60 Bullet Drop (Inches) 1,702.18 1,650.09 1,601.51 Impact Energy (Foot Pounds) 715 753 793

Clearly, this load performs better as the temperature rises. The bullet impacts about 50” higher (i.e. flatter trajectory) for every 20 degree change in temperature. And it retains about 40 pounds more energy upon impact as well.

 

Barrel Temperature

 

A second effect that results from warm or cool outside air temperature relates to how hot your barrel becomes during your relay.

 

On a relatively cool day (50 degrees), the outside air is able to absorb more heat from the barrel at a faster rate than it does when the air temperature is or 90 degrees. This helps to keep the barrel cooler with fewer harmful side effects like “baking” the fouling in the barrel which in turn can result in a significant loss of accuracy.

 

Even on a moderate day (60 degrees) the barrel can become too hot to hold during the course of firing the 20 to 25 rounds that your relay may require, including sighter shots.

 

Ammunition Temperature

 

Heat — especially excess heat — can play havoc with your ammunition. Handloaded BPC ammunition that has not been properly stored or protected from outside sources of heat or direct sunlight can suffer significant performance deterioration. Not only will the explosion of the black powder in the case produce different results, but the lube on the bullet may melt from the excess heat and flow under the bullet or into the powder column itself.

 

Even if you have taken the proper steps to keep your ammunition cool prior to coming to the firing line for your relay, setting you ammo in the direct sunlight or chambering it in a hot rifle for any length of time can result in an errant flyer.

 

I always keep my ammunition in an insulated soft-sided cooler until I’m ready to transfer it into the ammunition block in the Shooter’s Tray that I carry to the firing line. In addition, the ammunition block that I use has a curved hood that covers the ammunition and keeps it out of the direct sun while I’m shooting on the line. Placing a white washcloth or towel over your ammo will serve the same purpose.

 

Shooter Temperature

 

Keeping the shooter cool and comfortable is an important element in the overall accuracy equation as well. If the shooter becomes overheated or dehydrated, not only does he or she become uncomfortable, but their physical senses are affected — vision deteriorates as moisture is drawn from the eyes and brain by outside heat, sweat running down the forehead can cause problems seeing the target, high blood pressure results from low water content in the body along with fatigue, weakness, lower back pains, inflammation, headaches, etc… — the list is a long one.

 

Staying fully hydrated during a match is very important for the shooter. Keep lots of bottled water (no carbonated beverages) within easy reach. Drink often during the day — don’t wait until you’re thirsty. By that time you are already dehydrated. It is not uncommon for some shooters to drink 4 to 8 bottles of water during the course of the day.

 

Humidity

 

Many shooters believe that humidity (i.e. the amount of moisture in the air) can have a serious impact on accuracy. The theory is that air containing a high degree of moisture must be more dense than dry air. As a result, it must offer more resistance to a bullet in flight than does dry air.

 

The fact of the matter is that the amount of humidity in the air has virtually no effect on bullet accuracy. That’s because a water molecule weighs less than a dry air molecule. Yes — that’s what I said. Moist air is actually less dense than dry air.

 

In fact, when the surrounding air is said to have 100% humidity (i.e. it is holding as much water vapor as it can at its current temperature), it still only contains 4% moisture. Look at the numbers for yourself:

Load Data — Caliber = .45-90 — Velocity = 1,300 feet per second — Distance = 1,000 yards — Ballistic Coefficient = .400

 

Humidity Level

0% 50% 100% Bullet Drop (Inches) 1,629.66 1,626.88 1,624.12 Bullet Speed (FPS) 800 801 802 Retained Energy (Foot Pounds) 769 772 774

According to the numbers above, the trajectory of the bullet becomes flatter (with less drop), travels faster (higher speed), and retains more energy upon impact (retained energy) as the air becomes more saturated with moisture.

 

It is true that a high degree of moisture in the air does help to keep the fouling in the barrel softer than on a hot, dry day. But about the worst thing you have to worry about when the humidity is high is keeping your gear dry and preventing it from rusting!

[gurtwurz 793]

cheers for that stevo, makes interesting reading. it doesnt explain why my pellets were landing high though, unless the air was so moisture laden due to the snow coming down that it made the air less dense?

 

but it rules out the cold air speeding the pellet up, as it were, and also explains why the pcp lads were finding their shots were dropping after 35m

 

could it be as rake put it that its due to denser air in the chamber behind the pellet, therefore maybe being in effect slightly compressed and pushing the pellet harder? be worth checking the chrono next time its cold enough, as typically, its warmed up round here now...

 

cheers, wurz

[secretagentmole 1,701]

Perhaps the wires that formed your cross hairs shrunk? Only works with old fashioned cross hairs and no modern etched ones, unless your mounts contracted, reducing the height between scope centre and barrel!

Might lift it up a little bit!

[Buster321c 1,010]

That's nearly as good as your post on airgun forum saying that you frequently shoot and take quarry at 70yds.

[gurtwurz 793]

and the scopes a hawke airmax sr12 so its not that old moley.

 

cheers, wurz

[PIL 7]

Hi wurz ,good post mate .

Just to let everyone know I was shooting same comp with my AA s400 .177 zero'd at 35 yds and on a normal day I know 45 yds is 1 mil dot hold over but due to -8 and being hft inexperienced should have given the shot an extra half mil dot .I noticed a slight difference on the plinking range but not to the degree that I missed the kill zone at 45 yards in the actual comp .

It could do with someone with a chrono as been said in a colder climate to experiment and print results .

Hope this is legible as I'm writing on the phone

 

Sorry wurz I didn't see headline "springers" oops

Edited February 15, 2012 by PIL

[secretagentmole 1,701]

That's nearly as good as your post on airgun forum saying that you frequently shoot and take quarry at 70yds.

 

Buster the crosshair comment was a joke, and I did not say I frequently take quarry at that distance, but that I had and I often shoot targets at that range to keep the knack of how to do it.

[Buster321c 1,010]

It is perfectly possible to get a shot that kills at 70 yards, I have done so many times. My rifle is up to the job, in sub 12, do not feed FAC for hunting at a range of sub 75 metres (82 yards). Just use a good sub 12 and a decent pellet

 

And if you do not like the fact that people can and will take and make such shots, pull your head in!

 

 

 

 

Just quoted you there Mole , in case you forgot what you'd said .

Edited February 14, 2012 by Buster321c

[davyt63 1,845]

Hi wurz ,good post mate .

Just to let everyone know I was shooting same comp with my AA s400 .177 zero'd at 35 yds and on a normal day I know 45 yds is 1 mil dot hold under but due to -8 and being hft inexperienced should have given the shot an extra half mil dot .I noticed a slight difference on the plinking range but not to the degree that I missed the kill zone at 45 yards in the actual comp .

It could do with someone with a chrono as been said in a colder climate to experiment and print results .

Hope this is legible as I'm writing on the phone

 

Sorry wurz I didn't see headline "springers" oops

 

hi Paul

if you are taking a 45yd shot with 1 mildot hold under,then you will miss the plate completely

you should be using hold over

 

bloody armatures

 

Davy

[PIL 7]

davyt63, YOU WIN AGAIN :icon_redface: :icon_redface:

 

CHEERS FOR THE HEADS UP LIGHTHUNTER :laugh: :laugh:

 

Lesson learned beer +pc = feckup :laugh: :laugh: :laugh: :laugh:

Edited February 15, 2012 by PIL