CZ 455 and 452 less accurate in cold air?

[Marky]

Has anyone else ever experienced greatly reduced accuracy while shooting in cold air? Well, I entered my first 100 yard varmint shoot this weekend and I was embarrassed by my shooting. My grouping opened up from about the size of a quarter on my sight in target to about 4 inches by the time the contest was over. All of the other shooters experienced poor grouping but not nearly as much as I did. So, I  went home picked up my 452 (l used the 455 varmint at the contest) and went back to range to see if my problem extended to another gun (me or the gun or the weather)and it did! Just the weekend before I spent 3 hours at the range testing ammo and i was grouping 1to 1.5 inch this weekend. ...dud! Anyone else have this problem?

[painter]

I don't think the rifles are less accurate. I think it's the ammo.

Try keeping the ammo inside your jacket, and loaded magazines in your pocket.

[USMC Retired]

I'll bet it was the temperature of the ammo too. If a cold bore can change the burn of the propellent to throw off the round, then cold brass, led, and propellent in a warm bore probably does the same thing.   Here in southwest Texas it is usually mild and dry and seldom gets much under 40 degrees, but can get windy in the desert.  I try to store my ammo in a cool, dry location and try not to expose it to a drastically different environment up until it is loaded and fired. Although I am inconsistent in my shooting mechanics, with some decent ammo, in little to no cross winds my 455 HB is pretty accurate.  Its not too hard to shoot 1 inch groups at 100 yards in a gun rest, and on a couple of occasions I was able to shoot 3 round half inch groups.  I run into a fellow at the range on occasion who has an older 452 and he shoots consistent half inch to an inch groups out to about 125 with Wolf ammo.  But, this is almost always in conditions no worse than early fall in the midwest/east.

[Marky]

Hey Marine! nice to hear from you, I did some hunting around on the internet and found some guys saying that the ammo needs to be kept warm( some used hand warmers to achieve this) Unless, your shooting some expensive stuff like Lapua X( the guy that won was using LapuaX) the temp. affects the chemical reaction in the gun powder and the lubricant on the bullet. I was using CCI green Tag and needless to say t's not as good as LapuaX.

[USMC Retired]

Hi Marky,
Thanks for bringing up and reminding me of the issue. We are experiencing a cold spell over the past few days, and I remember seeing wider groups with my wieght sorted Win CPHPs in a recent outing.  I attributed it to a bad lot of what is somewhat marginal ammo in my 455 past 50 yards.  Perhaps the temperature had something to do with it instead, or both bad lot and cold conditions. 
Recently, I have had excellent results with Eley Target, Eley's least expensive offering where I buy.  One hole, 3 and 5 round groups at 50 yards, and a couple of half inch groups at 100. I am not steady enough to justify the more expensive Match ammo.  I don't see any difference between their Target and most expensive Match, but hopefully, at some point I will.  CCI Green Tag shoots pretty well, but I can get the Eley Target for about about $2 less per 50 rounds.  Green Tag seems to perform even better when weight sorted.  There is enough of a weight range in a 100 round box for it to make sense to me.   There does not seem to be enought of a range in rim thickness to make it worthwhile to sort Green Tag this way.  Win CPHPs vary quite a bit in weight and rim thickness, so when I sort by both it becomes an acceptable 50 yard target ammo at my current skill level.  Mark

[viking499]

Could the idea of keeping the ammo warm also have to do with the lube or wax that the bullet is coated with?

[USMC Retired]

Viking,

Makes sense to me.  There is probably a temperature that the grease or wax starts losing its viscosity in addition to the problem of cold propellent on burn rate dynamics.  Yesterday, I left my ammo on the dashboard of the truck for a few minutes with windows rolled up in the sun.  I did not notice any difference from the day before with similiar temperatures, but I figure that it was not anywhere near cold enough to effect burn rates or viscosity.

[horseman]

After doing an accurizing job on my 452 Varmint, three consecutive groups measured .16, .25, and .37 at 50 metres and the weather was freezing.
Next time out with temperature near 10 degrees C. (50 F) it would not duplicate and never did again.

[USMC Retired]

Have you tried polishing the bore?  It seems to help my 455 22lr.  I use a rifle rest and have found that keeping the rifle level both front to back and left to right makes a difference.  I also try to elimate paralax error even for short distances.  These things with more consistent trigger mechanics have enabled me to shoot one hole 3-5 round groups pretty consistently at 50 yards, and 100 yard 1 inch groups a little less often.  I am doing this with Eley Target, CCI SV, CCI GT, and on occasion Winchester CPHPs.  None of the super expensive stuff has been needed yet.

[Marky]

Hey Marine, what did you use to polish your barrel? I have another shoot next weekend and I'm hoping for calm winds. I don't think cold air will be an issue this time because we are getting into the warm season here, finally!