We just had our first outdoor match of the year. I checked my zeros first thing before the match. A couple of them were a click off of my standard 70F zeros. The temperature at beginning of the match was 57F. As the match went on a storm front moved in and the temperature dropped from 57F to 43F. At the end of the afternoon I missed five rams in a row causing some caustic subvocal abuse. I just couldn

Thinking metallurgically, my best explanation lies in the fact that the barrell's inside diameter will be slightly smaller in cold weather as compared to warm weather. Smaller diameter equals more bullet friction = changed zeroes.

My 2 cents,

SteveM.

Temp can change trajectory, for sure. Some ammo is more sensitive to it than others. Wolf Match Target drops velocity in the cold like crazy, and I've tested this myself. I'm sure other ammo does to varying degrees, too. I haven't ever heard of barrel constriction being a reason for changed zeros in the cold, but it can definitely affect ammo.

Well, you've pegged the ammo. It is SK Jagd Standard Plus, in other words, Wolf Match Target!

Nice to hear at least that someone else has noticed this. If the temperature is affecting the powder then I'll keep records but now I know to test the zeros for this ammo at different temperatures.

I was hoping some one else had taken some zeros at different temperatures and could clue me in on whether the weather could change my zeros by a minute or a half minute of angle.

Does the difference in air density with temperature significantly change the trajectory of a 22LR at 100 meters?

dwl

I don't think it does to any significant amount. If it did, the ammo specifically designed to be less sensitive to temperature changes, like Eley Biathlon, would also be affected just as much as ammo that dies in the cold like WMT.

Btw.. my tweaked CZ 452 shoots the lots of WMT that I use into 5-shot groups averaging 1.2" at 100 meters in 65 degree weather. That opened up to 4"+ at ~22 degrees. I don't know if it's the powder or the lube or what. I know it all went to hell in a hurry. Even the Eley Sport (Aguila in an Eley box) shot a lot better than the WMT in the cold.

The change in air density will make a difference- But I have no way to say how much. I have no doubt what you observed is real- but to seperate out the various factors involved would be very difficult. In addition to the velocity change due to the powder burning at a different rate in the cold you also have the relativly heavy lube used on most target 22 ammo.

Last fall sighting in for a match I was seeing a drop of about 3 moa with the first shot, and about half that with the next. The remaining shots were close to my original zero. This was with an ammo lot and gun I had been shooting all season. If I let the barrel cool I had to start over. What I did that match was hold high for the first shot, lower on the next and then back to my original zero for the remaining eight. This led me to buy some Biathalon ammo and try it. I did not see the zero change with subsequent shots with the biathalon ammo and shot it over the winter.

I ended up shooting the same biathalon ammo at Benton last weekend- with the same action- but in a new stock which is still not actually finished. Due to the amount of wind I do not know how it actually groups in the new stock- havging never shot it when it was calm. I suspect at Benton I may have seen the same thing happen as with the other ammunition- but in reverse.

I shot my hunter gun in standard class- which was shot in the AM. I ended the first match on the turkeys. After a bit they opened the range back up to warm up for the hunter match- which I would start with shooting the Turkeys. I wanted to double check my zero and so shot at one of the Turkeys off the bench- and did not hit it. I did that two more times- then spent some time adjusting the sights trying to get rezeroed. So after hitting 11 of 15 turkeys in the AM I could not hit them at all OFF A REST!??? After adjusting the sights some I seemed to be on again- but then when the match started I was not hitting when I thought I would be. Thanks to Mat Johnsons excellent spotting I knew some of those that were hits were not where I thought they would be, and I adjusted the sights after the first 5 turkeys. I ended up with 9 of 15 turkeys in the afternoon- close to the 11 of 15 I had shot in the AM. My guess is it somehow is related to the time between when I was shooting. I also know that if this was the case- shooting 15 would average the score upwards vs shooting just 10. I know one thing- I want to learn a lot more about what is going on in this area. This is also why I ALWAYS check my zero on paper before a match.

http://www.benchrest.com/forums/showthread.php?t=31121

I ran across this on Benchrest Central- rinfire benchrest.

I am sure they are a lot more picky about group size than we are- but I am sure there are thinks we all can learn from them.

It would be very confusing to be switching ammo mid match as it warms up.

just anecdotal... long time ago i took tenex and rifle match to the range on a plus 100 degree day. the club had a fridge and freezer as well. put a box in the sun on a black metal plate for 1 hour and a box in the freezer for the same time. found no difference in point of impact between the two.

Some ballistics expert types say that the important factor is the temperature of the barrel. For the purposes of internal ballistics (before the bullet leaves the barrel) heat and pressure are virtually the same thing. The hot, expanding gas not only accelerates the bullet, it warms the barrel. That is, heat is drained out of the gas by the cooler steel. The colder the heat sink, the more energy is stolen from the bullet's propulsion.

Another little tidbit for this conversation... A few days after that match where I had the WMT shoot so poorly, I went back to the range to do some testing. It was about the same temperature as during the match and the Wolf ammo shot just as poorly as it did in the match. I put a box in my pocket with one of those little disposable hand warmer packets in there for an hour. It shot the same as the ammo that had been sitting out in the cold, even though it was so warm the the lube had gone extra shiny from being what I assume is fairly close to its melting point. That leads me to think that it's the temperature of the layer of lube in the barrel affecting the bullet moving through the barrel or the temperature of the barrel itself affecting powder burn rate. I hope I don't have to shoot in the cold again anytime soon to test that theory, though. I hate being cold, and being from Alabama, I feel like I'm always wet and cold up here in rainy western Washington.

Thanks for the observations. I've been busy for a bit with work and repairs on my rental so I haven't had a chance to check zeros at different temperatures. I will do so and report back what I find. I'll probably test some different ammo as I have some Fiocchi and Lapua Master. Might order some Eley as well.

By the way, I checked with two other shooters. One reports having no problems shooting Wolf MT in the cold. The other reported an 8 click (2 minute!) drop. I know that when looking at the impacts on the target that my shots were hitting low late in that last match. What's a poor shooting oaf to believe?

dwl

Just take rests with you and verify the day of the match immediately prior to the match. You can verify that travel hasn't knocked your scope off zero, that your scope is tracking correctly, and that your rifle is functioning correctly, as well as checking for a bunch of other weirdness like cold zero change. While you're checking, make sure to use all the magazines that you plan to use during the match. I do sight in to get my click chart before match day if possible, but I also check them immediately before the match. I have enough trouble keeping my head clear without worrying about my scope zero not being correct or other equipment worries.

Just a couple of 'two cents'es:

Yes, I did observe a change in velocity with temperature on
my centerfire loads, and a difference in .22 Federal Lightenings
left in the sun vs. fresh from the trunk. (Playing with a chronny).

I question though whether initial temperature of a rimfire round
is very significant as with the large ratio of chamber mass to
cartridge mass, and the high conductivity of the brass would tend
to bring the cartridge temp. to barrel temp. pretty quickly.
Probably substantially completely during a long hold.
Has anybody any observations on cold barrel vs. hot barrel results?

As a student pilot, (when pterodactyls filled the skys), I learned that
air density, (as it affected aircraft performance, and by extention, bullet flight),
changes a lot with temperature/ humidity and that humidity
generally drops with temp. further increasing the density.
Perhaps this is a bigger factor in change of impact point than barrel/cartridge temp..
( Increase in density also increases the sonic velocity thus changing
where the 'buffet` occurs which might explain why some shooters
observe an increase in group size.)

Irv

I don't have any idea whether the pre-ignition temp of the POWDER (as opposed to the brass) makes any difference whatsoever but I do remember a comment by the great XC Highpower champion, Mitchell Maxberry, when asked whether he worried about a round "cooking" in a hot chamber: "Nope. Powder is an excellent insulator."