Thread: Velocity Loss From Summer to Winter.

Originally Posted by sneeze

Scribe put simply the ambient temp makes the powder warmer or cooler. Warm powder will burn faster than cold powder creating more pressure which intern creates more velocity.There are plenty of variables involving powder types,double base vs single base, burn rates,etc, I personally think barrel and chamber temp has an impact as well but its not something Iv given a lot of thought to. Some people (including myself) carry their ammo in a pocket close to the skin to try and keep it close to body temp in cold conditions, it helps.

Surely that is what I just said as simply as possible ?

Originally Posted by Scribe

Well there you go now, I know what you were talking about. All the time I was thinking outside the rifle, air density, viscosity, moisture and so on and so on. If you guys go on stretching the ranges onwards and outwards you will have to calculate earths rotation into your figures like they do with the long range artillery. Just kidding.

Thanks for that information.

They allready do Scribe (I dont cos I cant shoot far enough to warrant it)

Stop the world I want to get off now. Getting too complicated. A least the deer would get a good feed in before I figured out all the equations.

Originally Posted by Scribe

Stop the world I want to get off now. Getting too complicated. A least the deer would get a good feed in before I figured out all the equations.

Originally Posted by veitnamcam

Surely that is what I just said as simply as possible ?

Yeah pretty much, I hadnt read your post I just scolled down till I hit scribes question that I asumed was directed at me then hit reply.

Corriolis is a factor that has to be considered in some situations as well Scribe.

Originally Posted by Scribe

Stop the world I want to get off now. Getting too complicated. A least the deer would get a good feed in before I figured out all the equations.

All this would never be a problem for you Scribe if ya stick to your .223 and ranges under 300.

Originally Posted by R93

Corriolis is a factor that has to be considered in some situations as well Scribe.

Jesus that to huh.

Originally Posted by Scribe

Jesus that to huh.

Ha Ha, yup it is never ending.

Originally Posted by Im2lazy

If you're still there James and haven't committed suicide with all the advice you're been given

Here's another tip. Pop your bullets down your Y-fronts or in your pocket and keep them at 37.5 *C all year round. Just be aware that if you get the flu it might push the temp up to 39*C

-I'd been thinking about doing this.
But as I don't crimp or laquer my rounds, I'm a bit worried about the effect of all the bacteria and viruses on my powder. -probably mess with the burn rate as well...and then I'd be back where I started.

Originally Posted by sneeze

Hmmm bit condescending but you might be right. James I was wrong about the helicopter, apparently your going to need something really high to jump off.

...And I was just thinking about how much I was going to have to spend on an Ohler....
...Now I have to factor in an extra $400/hr per range session for chopper hire.......long-range just keeps getting more and more expensive

Originally Posted by Scribe

Jesus that to huh.

...and the there's "Spin Drift".....oh, the fun that's to be had. Lucky for most of us there are computer programs to get us in the ballpark first

Don't worry James, Knights Armamemt have a downloadable app for your Iphone/Ipod called "BulletFlight", it can factor Coriolis and Spindrift into your shot calculations.



Usually sighting your rifle in with 1/4moa of left dialed in will negate spin drift out to "normal" distances, i.e. anything under 800yrds !

From 800yrds to 1000yrds you will need an extra 1/4moa (for a total of 2 clicks) left to negate the effect of spin drift.



Coriolis at 1000yrds is easy to remember, shooting to the East your projectile can hit 3 inches high and shooting to the West your projectile can hit 3 inches low, a North shot can give up to 3 inches right and a shot to the South can give up to 3 inches left.

As with all variables, practice will determine if these two conditions affect your chosen projectile with its unique velocity/rpm and bc.

To be honest, you have to be a very good shot with a well dialed in rifle to notice these things, and hand on heart I have more trouble with light breezes/air movement than either of these two factors.

James, shots made at longer ranges need two more calculating factors, shot angle -which is self explanatory and R93 mentioned Air Density altitude and he's spot on, its very important. We won't mention wind induced vertical......

Example.

162 A-Max @ 3080fps. 200yrd zero. 12deg C. Zero shot angle. Target is 1344yrds (far as my old geovids went).

My Baro read 1013.20 Mb or 29.92 InHG so I needed 38.2 MOA (538.3inches) of elevation dialed in for a first round hit, -Sika only give you one shot on Ferny Ridge !

Now if we set/calibrate our Baro wrong and only read 982.05 Mb or 29 InHG I erroneously need 37.3 MOA (524.4inches) of elevation, - thats low by 13.9 inches, and a miss, one lucky deer.

I have a baro in my GPS, two small handheld baros and one in my watch, they all need to be set to measure AMBIENT pressure, thats the pressure where I'm standing, and be temperature compensated.

Air pressure and therefor density alters with the weather, even at sea level, and what we need to know is what the air pressure(density) is at the time and place we are pushing a projectile through it.

So carefully check the calibration on your Barometer with local internet weather stations and sync your readings, then check on the hill in different weather, once dialed in and measuring correctly you are on your way to understanding

the environment you are pushing a projectile out into.


Put it this way.

We learn about the recoil pad, the stock, the receiver, the bolt, the firing pin, the primer, the brass, the powder, the projectile, the barrel, then the air it flies through and atmospheric variables, then terminal performance.

This makes us more efficient Target shooters. (Hunters)

Now we can muse over wind induced POI elevation effects, and how frustrating they can be.

And shooting at extreme angles at distances past 1000yrds, considering the air density changes in the projectiles flight path due to the elevation difference between shooter and target.

And the need to use stepped BC's as the projectiles velocity decays out past 1500yrds.


I might go for a bush hunt now, my head hurts....



Sorry for the thread hijack