Load Performance vs Ambient Temperature?

[wkdickinson]

I got a new MagnetoSpeed V3 from my wife for Christmas which I am dying to try out. I also recently finished reading Brian Litz's third (I think) book, which talks a lot about load consistency requirements for competition. I live in the Upper Peninsula of MI, so our temperature will likely be in the single digits to teens (+/-) for the next few months.

I realize MV's worked up at these temperatures will be significantly lower than when shot at summer temperatures. However, my question is will the ES and StdDev for a group be valid when scaled up to 70 or 80 deg?

 

[Bbear]

Most likely not. Temperature sensitivity varies based upon the cartridge. And, can even be based upon the lot of the powder. Some powders are more sensitive than others in some cartridges.
I noticed many of the Reloader powders are rather sensitive in the cartridges I've tried them in (all in hunting rifles). Where you have a lower cold temp than I, my summer temps can, and do, get into the 100's.
Today is a good example of a 'typical' winter's day - low of 35, high of 65. Some powders in some cartridges will seem to almost freak out with that type of change. If you load and find a good load in the single digit temps you youpers have, you may find you need to drop 1/2 - 1 grain to stay the same when you get into the 80's and 90's.

 

[wkdickinson]

I'm sorry I neglected the specifics -243 Win, 105 Berger Hybrid, H4350, 210M. I understand the relationship between temperature and pressure/velocity, that is not my question. What I want to know is the likelyhood, of a load that has an 8fps StdDev at 10 deg, will have the same at 75 deg?

 

[JFrank]

There's probably a fancy computer program that would calculate SD against temp changes.
I had an curious incident in November where I was getting heavy bolt lift in the morning that went away as the temperature warmed up. Here's the odd- my rounds where hitting higher on the target by 1- click'

Why higher??

 

[Milo 2.0]

There's probably a fancy computer program that would calculate SD against temp changes.
I had an curious incident in November where I was getting heavy bolt lift in the morning that went away as the temperature warmed up. Here's the odd- my rounds where hitting higher on the target by 1- click'

Why higher??

I can't explain heavy bolt lift in cooler temps, that may be something to look into.
As far as hitting high with the same load in the afternoon, as it warms up, the air gets thinner and your bullet flies better, it's called density altitude. If the morning you were shooting in was a bluebird morning, warm and nice, and then a serious cold front came in at noon, and temps drooped fast, now your bullet may impact low. A cloud passing over you and your target(if at distance), it can change your vertical impact also.

 

[Milo 2.0]

I'm sorry I neglected the specifics -243 Win, 105 Berger Hybrid, H4350, 210M. I understand the relationship between temperature and pressure/velocity, that is not my question. What I want to know is the likelyhood, of a load that has an 8fps StdDev at 10 deg, will have the same at 75 deg?

Smart money says no, that is a 65deg swing in temps. BUT< big but, your load depending on node or pressure range may get even better, or fall apart altogether.
I have loads with RL 17 and Win 748 that shine in warmers temps, but deteriorate in cooler temps. I've also had loads developed in the spring or fall become over pressure when it warms. It's over my paygrade to say which way yours will go.

 

[thatguyshm]

Living in Maine, we can get temp swings during hunting season so i always test my rifles two ways. My gun safe is around 65 degrees, so I'll head straight to the range and test accuracy and then put the mag speed on and check velocity.

Then I will wait for a cold snap before the season, put my rifle and ammo in the garage the night before and head to the range nice and early and do the same thing. Usually ammo and rifle will be in the 20s to 30s. That way I can check cold bore accuracy and velocity at both weather ends. I find a cold gun and ammo is more realistic to hunting conditions than just cold ammo.

 

[Billy 30-06]

I would not load more than you plan to shoot at those temps. You will have to use your chrono to work up another load when the temps get much warmer. Your SDs should be close to the same when loaded to the same velocity.
You will find your chronograph to be a useful tool.
Around here I don't normally shoot in temps below 35*F or above 90*F. With Varget or H-4895 in my .308 it takes 2 or 3 .10s change in powder charge to put the velocity back where I like to keep it.
Billy

 

[BCBRAD]

I'm sorry I neglected the specifics -243 Win, 105 Berger Hybrid, H4350, 210M. I understand the relationship between temperature and pressure/velocity, that is not my question. What I want to know is the likelyhood, of a load that has an 8fps StdDev at 10 deg, will have the same at 75 deg?

There is a good chance it will maintain the ES & SD if the load is very close to the OCW. An OCW load will be tolerant to small-ish changes in loading parameters as well as temperature.

I find about 1/2gn of powder up /down to maintain tune in temperatures that range from well below zero to ~ 75 F.

Also, with the information from your velocity, you will be able to load for expected temperatures. For hunting I load for 40F, targets and competition I try to guess what the temperature range will be on event day/s

So, shoot a string on cold days and then on hot days check differences in velocity and charge accordingly.

 

[10XSHOOTER]

A load you make in July can be shot year around. A load made in January can only be shot in colder weather. Here in Colorado that's the formula to go by.
Doesn't matter what powder your using. Temps -20 to 100+ Crono is your best friend.

 

[Ned Ludd]

I'm sorry I neglected the specifics -243 Win, 105 Berger Hybrid, H4350, 210M. I understand the relationship between temperature and pressure/velocity, that is not my question. What I want to know is the likelyhood, of a load that has an 8fps StdDev at 10 deg, will have the same at 75 deg?

Shooting a load at a temperature 65 degrees warmer than when it was developed is very similar to adding half a grain or so more powder to the case. Do you think the ES/SD would have remained the same at 10 degrees if you added another half grain of H4350 to the case? There is really no definitive answer to your question that is anything more than opinion. What happens to the ES/SD all depends on where the load ends up relative to optimal at the new temperature in terms of pressure, velocity, etc., in your specific setup.

 

[wkdickinson]

Thanks everyone! I know there is no "answer", I was looking for informed opion, hopefully from experience. I should also have said this was for target work with a Savage Target action, 1:8" Criterion barrel, McRee chasis, Vortex GE. I have been reloading for 40 years and seriously shot NRA HP (Master) 20 year's ago.

My plan is too test 20 rds of the same load at 10 deg, 50 deg and 75 deg. I will report the results here, in 6 months. Thanks again!

 

[Terry]

One thing you might learn now is the velocity your rifle likes with a specific bullet.
You will reduce your powder charge as temperature increases to return to the desired velocity.

 

[topclass2017]

great thread with lots of relevant info.

As a longtime rimfire silhouette shooter in the Pacific Northwest, the problem was just opposite: in the winter, standard velocity (320 m/s, or around 1050fps) ammo always shot low at the 100 meter line by as much as 3-4", hence the development of "polar" or "biathlon" ammo of 340 m/s (1,115 fps). What I did was to keep my "summer" ammo in a container with one of those disposable handwarmers, and then once I loaded my magazines I kept them in my pocket that also had a handwarmer. I had no issues and didn't have to adjust my scope's zero.

So with that in mind, a couple of questions:

1. what about keeping ammo in a cooler in the summer (I now live in Texas)? I understand the issues of moisture on a cold round exposed to warm, humid air, and how quickly a round can heat up in a hot chamber.
2. Is temperature sensitivity about the temperature of the round/powder, or the ambient temperature when the powder is ignited? Going from 1/4 to 7/8 retired I've had time on my hands to do a lot of reloading and load development this winter. Many days in Central Texas have been in the lower 30's when I've been at the bench, so I understand that loads I've worked up this winter will need adjustment come the middle of summer.

 

[Bc'z]

There's probably a fancy computer program that would calculate SD against temp changes.
I had an curious incident in November where I was getting heavy bolt lift in the morning that went away as the temperature warmed up. Here's the odd- my rounds where hitting higher on the target by 1- click'

Why higher??

Because of the condensation created higher pressure causing shots to impact high