Here is the scenario: I developed a load for my 308 hunting rifle (39.7gr IMR3031, Berger 155gr VLD, CCI BR2, Nosler brass). At the range I kept my bullets in the running vehicle along with the rifle, and only took them out right before I was going to shot my group. The 5 shot group hit very close to .5 MOA when I first tested it and the temperature was about minus 4 with a very slight wind, range was 100 yards. The gun and bullets didnt have any time to cool off, as far as I can tell. So the next day I tried again and the group opened up to 1.65", and the same thing today!!! I used the same procedure (warm rifle/ammo from the vehicle). The only thing thats changed is its cold now, about minus 23, and light snow falling. Now I know what some of you are thinking, its the shooter, and perhaps it is. However, I used a front and rear sand bag while testing loads, and have practiced trigger control in the cold, plus I'm dressed for the cold weather, so I dont think its me. My question is this: Will the flight of a bullet over 100 yards be affected this much by cold weather and light snow, or is this more likely a rifle bedding issue or something to that affect?
Cold weather and accuracy
- Thread starter datatools
- Start date
some quick research indicates that your powder is regarded by many to be sensitive in cold weather. Heat seems to be ok, but the cold causes problems.
Check out the manufacturer or their web page for specifics... or someone who has loaded with it extensively, which I have not.
I use IMR 4064. I use 40-44 grains with Federal BR pimer and a 168 gr MatchKing HPBT. So far so good.
0.5-1.0 MOA @ 100 yards on a good day. Mind you it is a semi-auto, so a bolt would likely be better or more consistent.
Good luck!
Check out the manufacturer or their web page for specifics... or someone who has loaded with it extensively, which I have not.
I use IMR 4064. I use 40-44 grains with Federal BR pimer and a 168 gr MatchKing HPBT. So far so good.
0.5-1.0 MOA @ 100 yards on a good day. Mind you it is a semi-auto, so a bolt would likely be better or more consistent.Good luck!
- Location
- Somewhere on the Hudson Bay Coast
-23, sorry I thought your were shooting in the cold.
Seriously though, the effect on the burning rate can result in a greater extreme velocity spread. Dense cold air effectively reduces a bullet's BC, and although BC doesn't normally have an influence on accuracy, when the BC is reduced, the bullet's sensitivity to wind increases; so at low temperatures a slight breeze has a greater influence on the drift of your bullet.
You dress in bulkier clothing in the cold weather, and this can effect your LOP, your eye relief, and if your eye is properly or consistently aligned with the scope. You may have inadvertently introduced a parallax problem. If you wear gloves to shoot, or if your hands are cold enough that you loose sensation in your trigger finger, you might not be as precise on the trigger as you would normally be. All of these things, individually or combined, can degrade accuracy, or at least our ability to achieve an accurate shot.
Seriously though, the effect on the burning rate can result in a greater extreme velocity spread. Dense cold air effectively reduces a bullet's BC, and although BC doesn't normally have an influence on accuracy, when the BC is reduced, the bullet's sensitivity to wind increases; so at low temperatures a slight breeze has a greater influence on the drift of your bullet.
You dress in bulkier clothing in the cold weather, and this can effect your LOP, your eye relief, and if your eye is properly or consistently aligned with the scope. You may have inadvertently introduced a parallax problem. If you wear gloves to shoot, or if your hands are cold enough that you loose sensation in your trigger finger, you might not be as precise on the trigger as you would normally be. All of these things, individually or combined, can degrade accuracy, or at least our ability to achieve an accurate shot.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
IMR3031 is a temp sensitve primer. If you have a fussy rifle, you will need to adjust your load every 10C to maintain tuning.
why we don't shoot this type of powder in competition. We can have a 20C temp change over the course of a day.
When it is that cold, your primer will also loose spark. Magnum primers will help.
Not as big as deal when you have full spark but a low load density charge can have ignition problems as well
Try some Varget and you will likely end up with a load 42 to 45gr (43ish is likely a sweet spot). That will fill the case pretty much to the base of the bullet so the powder cannot slosh around. This ensures what spark is there WILL ignite the powder.
This powder is very stable over a very wide range of temps BUT you still need to tweak your load between a summer load and winter load to maintain tuning.
I use alot of CCI BR2 primers but avoid temps below -10C as I am a wuss and don't like shooting that much
Don't discount the affect of cold on the rifle too. Maybe the bedding/stock is changing. Maybe the scope is moving??????
But the easiest is to play with primer and powder and get a baseline.
Jerry
why we don't shoot this type of powder in competition. We can have a 20C temp change over the course of a day.
When it is that cold, your primer will also loose spark. Magnum primers will help.
Not as big as deal when you have full spark but a low load density charge can have ignition problems as well
Try some Varget and you will likely end up with a load 42 to 45gr (43ish is likely a sweet spot). That will fill the case pretty much to the base of the bullet so the powder cannot slosh around. This ensures what spark is there WILL ignite the powder.
This powder is very stable over a very wide range of temps BUT you still need to tweak your load between a summer load and winter load to maintain tuning.
I use alot of CCI BR2 primers but avoid temps below -10C as I am a wuss and don't like shooting that much
Don't discount the affect of cold on the rifle too. Maybe the bedding/stock is changing. Maybe the scope is moving??????
But the easiest is to play with primer and powder and get a baseline.
Jerry
Targets
Here is a couple pictures of the targets. I've seen my groups open up before from minor issues (ie: different powder, different day, different bullets,bad shooter day, etc...), but this has me scratching my head. This is why I love shooting. What fun would it be if we shot one ragged hole groups every time we went out!
Day 1:
http://img703.imageshack.us/i/img0135kq.jpg/[IMG]
Day2:
[IMG]http://img340.imageshack.us/i/img0136qq.jpg/[IMG]
If these pictures dont appear, would someone please tell me how to post pics properly. Many thanks.
Here is a couple pictures of the targets. I've seen my groups open up before from minor issues (ie: different powder, different day, different bullets,bad shooter day, etc...), but this has me scratching my head. This is why I love shooting. What fun would it be if we shot one ragged hole groups every time we went out!
Day 1:
http://img703.imageshack.us/i/img0135kq.jpg/[IMG]
Day2:
[IMG]http://img340.imageshack.us/i/img0136qq.jpg/[IMG]
If these pictures dont appear, would someone please tell me how to post pics properly. Many thanks.
If it makes you feel any better. A few weeks ago, shooting 155 VLDs, 45.7 varget at 200 yards, 5 shots, I was getting groups <= 1 inch. Weekend before last it was about minus 14 and the groups opened up to >=2 inch. I don't know why.
Here are your pics.
Click on embed the image and then cut and paste the entry for Forum.
Uploaded with ImageShack.us
Uploaded with ImageShack.us
Here are your pics.
Click on embed the image and then cut and paste the entry for Forum.
Uploaded with ImageShack.us
Uploaded with ImageShack.us
Take 2 trying to post pics:
Day 1:
Day2:
OK, I got the pictures to appear. So heres a little more to the story. I tried 3 different loads on day 1, same powder and bullet, just different charge weights. As you can see, group C went to hell. I figured the added velocity threw out the harmonics and accuracy went out the door. Hence I went back the next day with the same load as group B, and now it opened right up (see groups B and C on day 2. Any thoughts??
Day 1:
Day2:
OK, I got the pictures to appear. So heres a little more to the story. I tried 3 different loads on day 1, same powder and bullet, just different charge weights. As you can see, group C went to hell. I figured the added velocity threw out the harmonics and accuracy went out the door. Hence I went back the next day with the same load as group B, and now it opened right up (see groups B and C on day 2. Any thoughts??
At 25C I need 9.25 MOA at 550 yards and then when the temperature was 0C I needed 11 MOA to get on target. Temps can definitely have a big effect on come ups and probably on accuracy. I try to keep a round in my glove when its cold and I'm hunting long range to minimize this.
Tossing out a little cold weather logic as well....your stock is going to expand/contract at a different rate than the receiver to which it is bolted. I would also assume it would effectively screw up your bedding job if the temperature changes too much.
More than likely its a combination of all the little things compounding to big changes though.
More than likely its a combination of all the little things compounding to big changes though.
Check this out http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2396060&gonew=1#UNREAD
This is a neat cold weather test a guy did.
Looks like bedding the action will help the cold weather problem out a bit.
This is a neat cold weather test a guy did.
Looks like bedding the action will help the cold weather problem out a bit.
First powder I ever tried in my .308 was IMR3031. Worked great all summer long. Then winter hit and I had the same problem as you.
Now I only use Varget, because it gives consistent velocities from winter to summer to winter. Only very minor tweaking is ever needed if you want exactly the same muzzle velocities.
Now I only use Varget, because it gives consistent velocities from winter to summer to winter. Only very minor tweaking is ever needed if you want exactly the same muzzle velocities.
The X-axis is temperature in degrees F (and yes, I did heat them that high, that is only around 77 deg. C), the Y-axis is velocity in fps.
The way the tests works is that you soak 3 batches of ammo at hot, cold and ambient temperature for at least two hours (5 rounds of each). I used a cooler with a heating pad for hot, the freezer in the clubhouse for cold (an icebox works too), and just sit the rounds out in the open for ambient. Temperature is measured with thermocouples and/or mercury thermometers.
You then fire them one round at a time in a round robin sequence (ambient, hot, cold, ambient, hot, cold...). You let the barrel cool in between each shot. When you fire each round, you just transfer that round from the hot/room/cold storage to the chamber and fire it through the chrono as quickly as possible. You don't want to give the rounds any time to change temperature internally due to contact with the chamber. I set the scope on the lowest magnification and just make sure I'm sending the round through the sweet spot of the chrono (no groups here). You basically want to the Jerry Miculek of loading a boltgun and firing it through the chrono. This is best done on a short pistol range, close to the berm.
It isn't a difficult test to run. However, if you don't have the ability to measure pressure (I do), I would advise putting the heating pad on a lower setting.
