Overheard an interesting conversation

[Working Man]

The jist of what I heard was in reference to stainless vs blued rifles and the difference in accuracy in cold temperature.

I have heard some back and forth that one is more inherently accurate (seemed more opinion than fact) then the other but I have read more definitive information that sighting in a rifle in a warm temperature climate then traveling to a cold temperature climate will require the rifle to be resighted in.

So I am faced with several questions.

1. Is there an inherent difference in accuracy between stainless, blued, and cast at room temperature?
2. Is there an inherent difference in accuracy between stainless, blued, and cast in cold temperature?
3. How much of a difference in temperature is required to make one have to resight their rifle?
4. Finally is the difference in temperature different for stainless, blued, and cast to make one have to resight their rifle?

 

[hammerklavier]

Don't forget chromed barrels also

I'm sure that there is a difference but suspect that it is slight.

The biggest difference is the difference between cold, normal and overheated.

 

[Working Man]

Another thing It made me think about was is there a difference in accuracy dependant in what the actual round is made of (hard vs soft rounds) under the same stipulations I mentioned above?

 

[Shadow 7D]

There is major differences, the same round hits difference places when the barrel is cold, and when the barrel is hot, that's a given, also the round performs different at -60 than at 60. So your question is does the composition of the barrel affect it's reaction to temperature, probably but only slightly compared to the effect of the temperature.

6" in an M-4 between zeroed at 25m @60f and zeroed at 25m @-60 multiply that by 12 to get the 300m target and you have a major drop about a 72" drop in 300m, but then you have the inaccuracy of shooting a VERY COLD barrel then shooting a hot barrel, I saw target that had a straight line cut through the center. So in cold environments you basically either zero your first round, or zero a warm barrel and know that you will miss the first shot.

Oh and as far as I know, cast barrels went out with cannons, so I would hate to know what the H your shooting.

 

[gunnutery]

The whole blued vs. stainless thing (in reference to accuracy) has me a bit confused. Isn't that like saying painting racing stripes on a car adds horse power?

Besides, no two guns shoot exactly the same and the difference in finish cannot actually be compared. Unless you're saying to shoot said finished rifles at warm temp, then shoot at cold temp and let the difference in inches dictate the winning finish. I think this would have to be tried with numerous different rifles to accurately find the outcome.

 

[Steve Marshall]

There is no difference due to the material of the barrel. The coefficient of thermal expansion are in the same ballpark. Stainless tends to have slower feeds and speeds when machining but that's about it. By the way, you can't extrapolate what happens to several hundred yards as opposed to being sighted in at 25. Just one minor example. You may not even have crossed the line of sight when zeroed that close.

 

[CB900F]

Fella's;

And, and, let us not forget the ammunition. There exists a large body of information regarding the effects of temperature upon the burn rate of various powders. It would seem to me that unless the testing for temperature affects on barrel material have completely isolated the ammo, you're not going to get any valid results.

Frankly, I think that this whole thing bears a remarkable resemblance to questions such as: "How many angels can dance on the head of a pin?", but that's just me.

900F

 

[bill in IN]

If the ambient temperature change is significant, the zero will change....

 

[MMCSRET]

I lived in Hawaii for several years and did a lot of recreational shooting at the Koko Head facility on Oahu. I found the biggest factor in POA to be humidity. Temperatures on Oahu are pretty consistent but the humidity changes drastically for dry season to rainy season. I had to resight scope sighted rifles with the season change.
I now live back in my home state with wide temperature sweeps and little long term humidity change and find that the only time I have to resight a rifle is when something physically has been changed, such as bumping, dropping, or retightening stock screws.
Of course every gun is an entity to itself, so generalizations have many exceptions.

 

[SSN Vet]

The coefficient of thermal expansion for austenetic stainless steel (300 series) is approx. 0.000009 in/in/deg Fahrenheit.

So one inch of stainless steel will expand 0.000009 inches for every degree increase in temperature.

The coefficient of thermal expansion for chrome molly steel is approx. 0.000006 in/in/deg Fahrenheit.

So one inch of stainless steel will expand 0.000006 inches for every degree increase in temperature.

The difference is 0.000003 in per degree.

But, internal stresses resulting from the machining processes will be different for the two materials, as they are cut at different feed rates and tool speeds. So when heated up, one may relieve more internal stress than the other.

The only way to really answer the question is to take to rifles that are identical, with the acception of the barrel metal, put them side by side in a test chamber and measure the barrel deflection as they are heated up.

Even if you do side by side testing at the range.... I suspect the test variables (wind, operator differences, etc...) that are not controlled exactly, will likely have more affect than the difference in the metals.

If there was a difference.... I'm sure one of the gun manufactures would be touting it as an "improved accuracy" bla, bla, bla in their marketing materials.

 

[Shadow 7D]

Steve, go read a military small arms manual on the M16 family, 25m is the zero point because that is the first crossing point... So while I give as an example, you are right that it is not exact, but it's in the ball park, you aint gonna pick up 10 MOA in the next 275m

And I believe that there is a significant decrease in velocity due to a slower burn rate and the cold effect on the bullet. As far a the differences between ordinance steel and stainless, probably not nearly as much as weather.

 

[mustang_steve]

perhaps this is a good reason to use a gun sock with some warming devices placed strategically within them. that would at least keep the rifle closer to the temp it was zeroed at.

 

[Steve Marshall]

Shadow, perhaps I misunderstood your post. I read it to be a 72" difference at 300 meters which is much to much. I would expect perhaps 3 or 4 inches. I used to practice my offhand in summer and winter and never saw more than 1 or 2 MOA at 300 yards. Here is some 2nd hand information? I was at the range the other day and a shooter was having major problems sighting in his new AR. In the course of conversation he asked what the ideal sighting-in range would be. I really didn't know but as I recalled it was in the area of 275 meters. A retired Gunny happened to hear this and indicated that Marines now sighted in at 200 meters and the first crossing occured just shy of 50 meters. So that is what the new owner did. Only thing was that the markings on the sight didn't correspond with the range shot.

 

[Shadow 7D]

If you were sighting for shorter range you would zero farther out, look at ballistic charts for 5.56, 25m and 300m line up. And yes I did say 6 feet of drop, and I'll stick to that because I was shooting that, 6 inches below aim point was my first shot, as the barrel warmed it picked up, but then it cooled, and dropped, 300m / 25 = 12, 6" x 12 = 72" so extrapolating the same way moa work gets you a 72" drop below what you normal POI would have been.

Now all things considered, with a warm barrel that approximates non arctic temperatures I could see, and did see less drop, but the problem is that there wasn't a consistent aim point, the cold barrel warmed and point of impact changes.

The snipers also mentioned that the mirage, which you do take into account of when you shoot, even if you don't see it, distorts light differently due to the extreme temps between the hot barrel and very cold air.

Steve, I see you're in New England, do you shoot when it's sub zero?
I don't, wouldn't have except my command was stingy and got the ranges cheap. They were located at Ft. Wainwright AK, and Donnelly Training Area, it was the middle of winter and the units stationed there were training in Australia and Ft. Irwin CA.

And finally, I believe that this topic has been very well covered by long distance shooters and as a matter of fact even has aps that are gun specific to guide your optics adjustments to account for local weather and climatic conditions and range.

 

[Steve Marshall]

Not quite sub-zero but the range of temperature was close to 100 degrees. And as I said, I never saw more than 2 MOA variation. This was with a Steyr SSG and a #4 MK1. Maybe we could get some High-Power shooters to chime in.

 

[Shadow 7D]

Thinking about it, you probably loose alot more power out of the shorter barrel of the M4 than a full size rifle in such extreme temps