TargetTalk

I am wondering what makes a rifle more accurate in cold weather or more correctly what causes some rifles to lose their accuracy less than others? Anschutz says their biathlon barrels are cold weather tested, but how do you make a barrel that performs better in cold weather? Is this a metalurgy problem? How much do the actions come into play? It would seem to me that some of the tolerences would have to be looser to allow for temperature changes. How do they do it?

pcw wrote:I am wondering what makes a rifle more accurate in cold weather or more correctly what causes some rifles to lose their accuracy less than others? Anschutz says their biathlon barrels are cold weather tested, but how do you make a barrel that performs better in cold weather? Is this a metalurgy problem? How much do the actions come into play? It would seem to me that some of the tolerences would have to be looser to allow for temperature changes. How do they do it?

I don't know about the other things to make it shot better in cold weather, but I would think you would want the tolerances to be tighter as metal contracts in cold weather. Ammo will play a factor as well as performance will vary at different temperatures. The other factor is the lube on the bullet can foul the barrel at the colder temperatures.

I would think that because of different contraction rates of different metals and the different size pieces, that tolerences would have to be looser. If a barrel had tighter tolerences at say 70 deg f, at 5 deg f would it even fire? Anschutz says in their biathlon catalog that their barrels are cold tested, but what is special about the barrel to begin with. I don't think that the biathlon rifles are as accurate as their precision models to begin with.

The reasons for my questions is that a Savage mk II can be restocked as a biathlon rifle, but the accuracy falls way off in the cold. I wonder if it could be rebarreled with something more suited for the cold, but what would that be and how would you know? If you were to make a barrel for the cold, what would you do differently?

I think it's mostly the ammo. See the link below. I do biathlon and my first year shooting at West Yellowstone was terrible. After discussions with others and reading on the web, found out the regular ammo may not shoot as well in cold weather. I then tried out various cold weather ammo, in -4 degrees F, and found a couple that worked well with my rifle - Fiocchi Biathlon V340, Eley Tenex Ultimate EPS, and Lapau Multimata. Had tried 2 others but didn't get good groupings. I usually use Federal Gold Medal Target.

http://www.biathlon.net/low_temp.html

This is where I purchased my cold weather ammo.
http://www.altiusguns.com/

Hope this helps. Good luck.

John

I think that the steel alloy they use may contain some element that reduces the thermal expansion/contraction of the steel.

This might make the barrel not group under normal room temperature (because of the additional properties that might come with the alloy), but when you vary the environmental temperature by a lot, then the overall grouping compared to a normal barrel could be better.

This is just speculation though…

Steel 13.0 (10-6 m/m K)
Lead 29.0 (10-6 m/m K)

This is the problem, there is a big difference between the expansion of Lead and Steel due to temperature. If you compare the differences in expansion of metals, Lead and Steel are about the worst combination you could have, they are at opposite ends of the scale.
A biathlon rifle is more than likely going to be shot at Sub zero temperatures so there could be 20deg+ difference between a Biathlon and a normal Small bore competition.

I would think a Biathlon rifle will have different tolerances in the barrel. Or bullets of a slightly different tolerance.

Back at the time that biathlon was converting from center fire to rim fire, Dieter Anschutz did testing of a number of barrels they were developing for the .22 cal. biathlon rifles. This testing took place at the Cold Regions Research and Engineering Laboratory in Lyme NH. He called in Creighton Audette, match rifle builder and metallurgist/machinist from Springfield VT to consult. He had a US Olympic Biathlete stand and shoot targets as the temperature in the large freezer room was lowered to test the barrels and the firing mechanism of their rifles. I don't know anything about the composition of the barrels they were testing, but their goal was to see where performance was best and where it dropped off using the controlled temperature drop of the giant freezer room at the facility. This was told to me either by Creighton Audette or by John Morton ( Olympic biathlete) of Thetford VT

Scott
Vermont

I'm not a metallurgist, but as others have said, I suspect they'll use tweaked alloys that are more stable across changes in temperature, as well as adjusting the tolerances appropriately for then the metal shrinks (making the bore slightly larger. It'll mostly be in the ammo - the beeswax on Eley match ammo for instance is going to be a lot harder at those temperatures, so ammo with lube and propellant designed to burn easily at those temperatures will play the biggest role.

I wonder also if the chilling and contraction of the barrel affects the harmonics at all? If so, then I guess the barrels would tend to be a different length to match barrels designed for shooting above freezing! Of course given the size of their hit/miss targets (not terribly small, although small enough when you're panting hard!), harmonics are probably relatively irrelevant given the tolerances involved. The rifle is probably fairly irrelevant compared to the ammo performing properly and the shooter holding still enough after they've raced a leg.

From what I've been learning elsewhere, it's the twist rate of the barrel and the velocity of the ammo that could make the difference.

Biathlon rifles use a 1:14" twist whereas an Anschutz Match barrel is a 1:16.5" twist. The faster twist stabilizes the bullet better at lower temperatures.

There also seems to be a particularly bad velocity for rimfire ammunition which varies with temperature - as the temperature drops, the Stability Factor of the bullet drops and accuracy degrades.

At 32 degrees F:


At 72 degrees F:


Check out the Border Barrels Rifle Twist calculator:
http://www.border-barrels.com/barrel_twist.htm

Ken.

Thanks for the replies. In regards to ammo, when I was at the Ethan Allen training center last winter, they were using some sort of sub sonic ammo, (I can't remember the brand, but they didn't seem too particular about it). The days I was there the temps were about 15 deg f.

In reading about biathlon rifles, it is stated many places that the Izhmash rifles were accurate down to about 20 deg f. Altius sells a rebarreled Ishmash that is supposed to work better. I don't know what kind of barrels they use, they may be Anschutz.

Savage MK II can be restocked for biathlon, but my understanding is that their accuracy drops way off in the cold. I wonder if they could be rebarreled and perform better. If someone were to try this what would they look for in a barrel? The information on the rate of twist in the barrel is very interesting. I hope ciscovt can give us more information about biathlon rifle testing.

The problem with Biathlon has been the 7-3 and 7-4 barrels. They are thinner than the 7-2 barrels. I built a 7-3 with a 7-2 barreled action. No problems with accuracy at -5F. This rifle will shoot .250 to .350 groups at 50 meters at normal temps with R-50. Not sure what the culprit is with the Ismash 7-3 and 7-4, but the 7-2 shoots fine in the cold.
Chris