Cold Weather Rifle Zero


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AR27
February 4, 2011, 01:12 AM
I want to zero an AR but the temps for this time of year were I live are usually well below 32 degrees. If I zero the rifle in this cold temperature will the zero be off in the summer when temps are around 72 degrees and higher?

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mc223
February 4, 2011, 01:48 AM
Your Zero might be different by summer, but not necessarily due to the cold.

Meaning if you very carefully transport the rifle to a resting place where it will stay undisturbed till summer, the Zero should not change.

Float Pilot
February 4, 2011, 02:41 AM
You only have to worry about a 40-60 degree difference.
Your barrel heat after being fired will change a lot more than that.

In some places up here it might be 65 below zero in winter and 85 above zero in the summer. A 120 degree difference.
But within 300-400 yards the difference in zero seems to be less than my own error... AS FAR AS THE RIFLE IS CONCERNED.

If you are hand-loading warm or hot loads in the cold of winter, they may produce a LOT more pressure after sitting in the hot sun of summer.

Some powders like the Hodgdons Extreme powders take that into account and seem to do really well with wide temperature swings.

If you have a heat sensitive barrel, like my lightweight Titanium 30-06,,, it will cool a lot faster at 10 below zero, than it does at 80 degrees above zero.

Generally speaking the AR platforms due pretty well with extreme temps as long as you sue the right type of lube.

mc223
February 4, 2011, 03:10 AM
So Float pilot is saying you do have to worry, because there is a more than 40 difference in temp.

You only have to worry about a 40-60 degree difference.

Float Pilot please elaborate.

WNTFW
February 4, 2011, 06:02 PM
AR27,
I would go zero it. Shooting in both condition is the only way to verify. Worst case is you would have to make some adjustment in the summer. Document it. Other thing besides temps cause POI shifts.

You don't say what ammo, specifically what powder. So someone would have to speculate more than anything. Even if they knew the powder speculation is still what it is. Some guys can speculate better than others.

Float Pilot seems to know what he is talking about.

"the difference in zero seems to be less than my own error... AS FAR AS THE RIFLE IS CONCERNED." That statement is something I can relate to.

Float Pilot
February 4, 2011, 07:23 PM
Float Pilot please elaborate. I meant that in his local conditions, according to what I thought he wrote,,,, he only had a 40 to 60 degree change in temps, which is not very significant.

The temperature of his chamber will soon be much warmer than the outside air after a couple 5 shots or so.

Should he want to leave his rifle laying on the dashboard of his car, on a hot sunny day,
Or shoot lots of rounds with a blistering hot chamber.....
I would suggest that he hand-load using one of the Hodgdon Extreme Powders.
Like: H-4198 or H-322, or Benchmark, or even H4895 or VARGET.

According to a common ballistics calculator:

If you fire a 62 grain bullet with a B. C. of .320 at 3,000 ft per second with a zero set for 250 yards and an impact at 500 yards.

At zero degrees F, at an elevation of 1,000 ft above sea level. 40.6 inches low at 500Y.

At 32 degrees F, same as above:

At 62 degrees F, same as above

at 100 degrees F, same as above

This is not exactly correct since it does not take into account DENSITY ALTITUDE.

Yes it does take into account regular altitude input. But not density altitude.

For instance at 15,000 ft above sea level, those same loads only drop 32.4 inches at 500 yards while the rifle is zeroed at 250 yards.

Because the higher air is less dense.

Density Altitude is how dense the air may be at any actual altitude due to the temperature and barometric pressure.

So, while you may be shooting on a wide open Illinois plain at only 800 feet above actual sea level, Warm temperatures and odd barometric pressure readings could make the air the same as several thousand feet higher. And your bullets will fly faster and further due to less drag.

http://wahiduddin.net/calc/calc_da.htm

You can usually get the barometer reading from the local airport automated advisory phone number.

As an example: If you are really at 1,000 ft above sea level, but it is 105 degrees, and the baro setting is 28.52 inches, then the air density is the same as being at 5,720 ft.
For us pilots that makes a huge difference on how well tan aircraft performs.

AR27
February 4, 2011, 08:24 PM
wow float pilot very informative, thank you.

Shadow 7D
February 4, 2011, 08:28 PM
Yeah, what float said, I have 'zeroed' a M-4 at -65, and lets just say it was an exercise in futility...

IF you know what you are doing... basically either you are looking for your COLD first shot, or are you looking for a WARM group?

mc223
February 4, 2011, 08:31 PM
The question is: If I zero the rifle in this cold temperature will the zero be off in the summer when temps are around 72 degrees and higher?

I see a lot of ifs and stuff that may be semi informative but what is the answer to the question.

AR27 do you have a scope or iron sights?
How do you normally store the firearm?
Do you use good quality ammo?
Did you get the firearm as a gift and the cold dang weather is making you crazy cause you just want to go shoot?

AR27
February 4, 2011, 08:34 PM
The question is:

I see a lot of ifs and stuff that may be semi informative but what is the answer to the question.

AR27 do you have a scope or iron sights?
How do you normally store the firearm?
Do you use good quality ammo?
Did you get the firearm as a gift and the cold dang weather is making you crazy cause you just want to go shoot?
1. Standard carry handle/A2 front sight (Irons)
2. In a wooden gun cabinet that I made
3. 55gr American Eagle brass
4. Nope

mc223
February 4, 2011, 08:42 PM
If you Zero it in the cold, I doubt with irons and cheap ammo that you would notice any change that may occur with temp.

Good Shootin!

35 Whelen
February 4, 2011, 09:06 PM
Here's a really good Ballistics Calculator (http://www.handloads.com/calc/) that will tell you.
I think your biggest concern would likely be with the ammo. If I'm not mistaken, most commercial .223 is loading with a ball type powder which is a double base powder. It's been my experience through chronographing that ball powder is affected quite a bit by changes in temps and velocities can drop substantially in cold weather. I ran into this with my 257 Ackley Improved that I was loading with WW760, a ball powder. I was losing close to 200 fps when shooting in 20 weather as opposed to temps in the 70-80 range. I recall reading a bookyears ago by...Bob Hagel I think it was...in which he tested various powders at various temps and almost without exception, cartridges loaded with ball powder showed a marked drop in velocity in cold temps.
Single base powders, which to my knowledge are always of the extruded type, on the other hand are not affected so much by changes in temperature. You might notice the Hodgdon "Extreme" powders that Float Pilot mentioned are all extruded powders.
35W

Shadow 7D
February 4, 2011, 10:19 PM
The question is:
Quote:
If I zero the rifle in this cold temperature will the zero be off in the summer when temps are around 72 degrees and higher?
I see a lot of ifs and stuff that may be semi informative but what is the answer to the question.



YES
but how you zero has a HUGE amount to do with it, if you zero with a HOT (to warm) gun, to zero a GROUP of shots, then it will vary less,
but if you are zeroing sniper, one shot, wait a few minutes, one shot
there will be a HUGE difference, the powder performs differently (you try a few delayed ignitions, and some of the other stuff that happens in extreme cold..)

AR27 do you have a scope or iron sights?
How do you normally store the firearm?
Do you use good quality ammo?
Did you get the firearm as a gift and the cold dang weather is making you crazy cause you just want to go shoot?

but yours WILL vary....
in how much it'll be off

mc223
February 5, 2011, 12:28 AM
Since the subject of the Hodgdon Extreme powders was brought up. Check the 0 pressures in comparison to the other two temps on the link.

http://www.hodgdon.com/smokeless/extreme/page3.php#top


Sorry it kinda makes the temp thing seem like a bunch of made up internet stuff. Yeah the testing was not done specifically on 223, but there are enough test to make it fitting.

WNTFW
February 5, 2011, 01:26 AM
http://www.hodgdon.com/smokeless/extreme/page3.php#308win

The info in the link also shows more spread in velocity and pressure in the competitors powder providing a reason the zero might change. Then again I bet RL15 has less spread if you look at the data Alliant provides vs what Hogdon says RL15 does.

If you read Float Pilot's post he says the POI is not affected using one of Hodgon's Extreme powders if temperature (0-100) only is taken into account. He even included the caveat about other atmospheric conditions and how to deal with that.

So far I would take Float Pilot or Whelen35's advice. Both gentleman seem to be truly helpful, genuine and spot on.

I don't think the OP stated a range, so at short range it would be a non issue.

Some things worth noting in the link is that velocity spread and pressure spread are not necessarily in direct relationship. Each powder reacts differently, so blanket statements are better avoided. Some powder drop velocity in the hot & cold variation. Some powders drop velocity in cold and pick up in hot. In the .30-06 VIT N550 the extreme spread is 12,600 CUP, which I would not take lightly. The ES is 49 f/s. The 4350 only has a 800 CUP ES but the velocity ES is 67 f/s. The link also does not provide a charge weight for each powder.
http://www.hodgdon.com/smokeless/extreme/page3.php#3006

So you can see why ignoring temps just because it is internet 'Made up stuff' might not all ways work out. Blanket statement don't apply to every situation.

TCU
February 5, 2011, 02:07 AM
being in illinois during the winter months, you will be under the influence of many pressure changing systems.

Shadow 7D
February 5, 2011, 02:26 AM
You're right mc :rolleyes: the whole cold thing is over rated, I mean whats the problem with military ball or any ammo for that matter, it all goes BANG

So what if it goes
CLICK---....Bang
it all goes bang in the end,

Now mind you that was in 'extremes' and in -65*F, but the point is, things can and DO behave differently

If you don't get it, you will be chasing your zero all over, first shot out of the cold barrel will be low, then it moves up as the barrel warms, so here's a question, are you talking
ONE shot, zero (BTW one of the few consistent ones you can get in extreme cold) or are you looking for a warm group?

mc223
February 5, 2011, 03:03 AM
Shadow 7D, I realize there are differences.:rolleyes: It does get kinda chily here in Wisconsin too.
You're right mc the whole cold thing is over rated, I mean whats the problem with military ball or any ammo for that matter, it all goes BANG
sounds like you have ammo problems. That I can help with as mine always go Bang.
I zero in winter. I shoot in summer. Regardless of all the words that went further and further from the OPs question.

Given the ammo the OP is using and the sights on the rifle as described by the OP, there are no factors that would change Rifle Zero.

Once rifle zero is set rifle zero does not change (until the OP changes it).

The ammo changes.
The temp changes the ammo.
The temp affects the shooter.
The barometric pressure changes.
Density altitude changes.
And I can not use density altitude at 15000 feet.
The OP is not using Extreme powders.
The Point Of Impact may Change.

The rifle zero is still unchanged.



Which brings us back to this:
Your Zero might be different by summer, but not necessarily due to the cold.

To those who might be offended. OH Well.

wanderinwalker
February 5, 2011, 07:58 AM
I want to zero an AR but the temps for this time of year were I live are usually well below 32 degrees. If I zero the rifle in this cold temperature will the zero be off in the summer when temps are around 72 degrees and higher?
Short answer: At common zero ranges, with the rifle and ammo you listed, don't stress about temperature swings. The cold is going to affect YOU more than the rifle and ammunition.

And I will say, I am very happy we rarely go much below -10 degrees around here! I've shot down to 0 degrees or so and never noticed a performance difference from my firearms. As for the shooter...

Edited: And my experience with the Hodgdon Extreme Powders is that Varget is stable as advertised. My heavy-bullet .223 match ammo runs to the same zeros at 25-degrees as it does at 100+ degrees on the shores of Lake Erie. Which is a huge confidence booster when you don't get sighting shots on a new range.

Picher
February 5, 2011, 08:38 AM
A factor in winter shooting with wood-stocked rifles: In cold climes, lower interior humidity in houses can cause wooden stocks to shrink considerably, loosening stock bolts and warping rifle forends.

In such rifles, pillar-bedding actions and especially, free-floating barrels can make rifles shoot much more like they do in the summer. Synthetic stocks are unaffected by humidity, but low temperature contraction amounts may differ from receiver/barrel steel. It's doubtful whether the slight difference would cause much variation in cold-barrel POI. Ammo variations and air density would probably be much greater factors than the small dimensional changes in the rifle.

I've not noticed any significant differences in POI of my synthetic-stocked centerfire rifles at 100 yards in winter. Rimfires are another story.

taliv
February 5, 2011, 12:41 PM
i don't usually see my 50 yrd AR15 zero change enough to matter, but i obviously see the trajectory at distance change with temp

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