Temperature changes and powders

[PJ1]

I'm learning the hard way for novice about temperature changes and powders. Curious as to what powders for 6.5CM, 308Win, 300 WM, 338LM that you are using that are less sensitive the temp changes in going from the house to outdoors in cold weather. What are best practices for ammo/gun when temperatures go from house(70-72 degrees) to outdoors(40-50 degrees)?

I ask this since I was using IMR 4350 ( due to scarcity of H1000 and H4350) and went out in 40 degree temp w/o allowing ammo to cool down. My groups were lousy as compared to 50+ degree days shooting 0.5MOA and less groups.................Like I said, learning the hard way.

Should load development always be done in hotter weather?

Thanks for your assistance.

 

[JEFFPPC]

Testing should be down close to the temp your interested in shooting. I find that one your getting beyond 15 degree up or down you need to adjust. Down seems to be worse than up.....I think. There is none that are temp insensative .Lin my testing. As with most things the best info will be from what you test.

 

[K22]

I hunt a year around, i.e., varmints in the spring / summer, predators, late fall / winter, deer, late fall. I practice all year around in varying temperatures.

What I learned, understanding that nothing is absolute and that I'm not an expert, but the following is my experiences.

1. Ball powders seem to be more affected by temperature changes than extruded powders especially in hot weather, i.e., temperatures 90 and above. I've experienced pressure surges with H380 in the 22 250 for example. Pressure surges are more concerning to me than POI changes thus I stop using ball powders for my applications many years ago.

2. Even with the so-called temperature resistance powders, I've experienced point of impact changes for even temperature changes as small as 20 to 25 degrees F. The reason I believe is due more to changes in air density, colder being denser thus harder to push the bullet down range than the powder's reaction to temperature changes. These POI's are not that extreme for the distances I shoot, i.e., under 300 yards. They amount to about 1/2 to 1 moa depending on the load / rifle barrel length / degree of temperature change.

3. Because I shoot a lot in varying temperatures, I'm familiar with how each rifle / load reacts and can make fine adjustments for more precision hunting applications such as varmint hunting. For example, in the spring with temperatures in the low 60's I know that the bullet will drop more as opposed to mid-summer when temperatures are in the 90+ range.

Bottom Line: To minimize the effect of temperature on POI, I use extruded powders. In addition, I shoot in vary temperatures and I know my rifles and the loads and how they will generally react to temperature changes. This in only an issue for precision varmint and predator hunting since the vital area is much smaller than big game.

Also, I'm fortunate enough to have several rifles so some I dedicate to predator hunting so I can avoid extreme temperature changes since there is less temperature extreme swings during predator season I hunt.

 

[Sniper338]

Your going to have to test that yourself. Get a good chrony.

Altitude will make a difference too if you move areas.

Alot depends on how far your shooting, if your hunting or target shooting...

Ive found several powders are fairly consistant with 1fps per temp degree in some testing ive done.

When i do that testing, I try to go get chrono data around about every 10 degree difference. May take a while to get the data recorded. Then you can make a chart and see the curve and the differences.

 

[RegionRat]

Should load development always be done in hotter weather?

Sure, if you plan on only shooting in the same…. just kidding.

Your post is more or less the answer to your own question in many ways.

You mention being able to get 0.5 MOA and then things in cool weather were lousy. This begs a question, how confident are you in that 0.5 MOA tune?

For example, the above advice that some, but not all, extruded powders are less sensitive to temperature is true. But then even you indirectly mention there may be a difference between IMR 4350 and H4350, which is true.

The real key advice going forward, is some of these powders are hard to get, because… they are in demand, because… they are far less temperature sensitive.

There is a reason ones like H4350 or Varget are always hard to find. They are very good to being with, but then when the days get colder or hotter, they take less work to tune. At the very least, their swing might be smaller, which allows folks to blindly adjust the charges a few tenths of a grain at risk.

Those with more experience in weather and travel, will test the tolerance of their tune in whatever weather they have, and then retest when they have the opportunity to verify a compensating adjustment.

Go back and test what you thought was 0.5 MOA when you get the chance. You have about a 50-50 chance it repeats. If it does, great, if it doesn’t you fell victim to statistics. Even if it works, go find out how sturdy that node is on the high and low sides. Borrow a chrono for at least recording the averages on those sessions.

Bottom lines: Powders are not all the same, it takes work to research the better ones and get them, it takes work to learn to tune to the nodes, and wisdom to select the one that forgives weather and wear. Get yourself a chronograph, but don’t obsess over it. Ballistics takes time and effort to learn.

 

[JMayo]

It isn't about the temp you work in in your house vrs what you shoot in.

It's just about what you shoot in one weather vrs another. Spring vrs summer, summer vrs fall temp change.

 

[Bill Norris]

As "forgiving" as H-4350 is claimed to be by Hodgdon I recently found in my 243AI and 107 gr. Sierra MK and shooting in 40 degree temp. changes (August to December) I had to adjust my E C tuner/brake from 10 in August to 12 in December in order to maintain the sub 1/4 inch 5-shot groups @ 100 yds. that it normally shot. This does parallel the theory of "down and out" with tuners meaning temp down - tuner out.

 

[Zero333]

6.5 CM - H-4350, RL-16, H-4831sc, IMR-4451
308win - Varget, H-4895, IMR-4166
300winmag - H-1000, H-4831, IMR-7977

338 LM - no idea except that many are very happy with RL-33 and even I use RL-33 in one of my 300winmags with 208 - 240 gr bullets and accuracy is awesome and never really cared about temp changes with it cause the width of the accuracy nodes is HUGE. with 240smk (no longer made) I had the same POI during load development spanning 100+ FPS, which was done at 220 yards.

 

[BillC79]

If you are shooting groups or shooting at a match, try to get your ammunition temperature equilibrated to shooting temperature as much as possible before you shoot. If you have 30 F degree difference between ammo storage and shooting, your ammunition in a storage box will equilibrate unevenly in the box. If you have a temperature sensitive powder, this will affect your impact spread considerably, especially beyond 200 yards when you are shooting groups or a string in a match.

Temperature effects on bullet velocity for various powders have been discussed. Two posts where this is discussed are HERE and HERE.

 

[D-4297]

Left out IMR - 4064 on the .308 list . One of the most stable powders you can run in a .308 , up to about 90 degrees F , and then you start dropping the load to keep the pressure down . But still extremely accurate when re-tuned . I shoot it year round at Ben Avery . From Low 30's to 110+ , in the Summer . But don't we all "Adjust" our loads thru the year ?

 

[Full Chisel]

I have yet to find a node in the rifles I load for that was good for more than about a 40* F window before groups start opening up or poi shifts too much. There is one exception, but it was a hot load, and I have run it over a 50* window with predictable poi change. I just dial with temp on that one and and don't adjust load. The others I just adjust like others have said. My rifles are not customs, and Im not using the extreme powders. I learned the hard way to verify final loads over temp range. On the last hunting rifle, I shot ladders at both temp extremes. Probably overkill, but it sure did paint a good picture. RL15, N135, N140, N160, IMR4831, IMR4895, LVR.

 

[Oso]

I'm in Texas and based on my weather pattern my greatest concern is extreme heat. As such I do a lot of load development in July - August when temperatures at in 95F-100F. If my load is toward max and safe at these temperatures then I am fine for every other time (temperature) throughout the year. I don't use powders that temp invert.

Every time that I shoot I bring out my Labradar. I always record temperature, velocity, and any wind. I either dedicate an entire page in my Reloading Book or add the data to a spreadsheet. This allows me to record the specific load and its performance over time... including at different temperatures. I can look at my log easily see changes in performance (velocity and accuracy) at different velocities.

The other great time to test/confirm a specific load is in December. If I pick the right week (Northern blowing through) I can shoot 10 shots at 65F-75F and then a couple of days later re-shoot at 35F-45F. Now, I have 3 data sets that cover the extreme temperature spread with roughly 20F-30F increments.

I like shooting in shorts in December with a light wind breaker. I like snow... well Snow Cones in the summer

 

[PJ1]

Great information and thanks for all of your help guys. I know this is a beginners question, but there is a myriad of powders out there and most of the better ones (h1000, h4350) are very hard to obtain.

I've now sunk down to StaBall, which has a checkered history from the little I have read, but it is one of the few out there these days. Plan to use that for 6.5C.

One seems to see more light at the end of the tunnel with supply, but you still have to be at the right place at the right time............Pray the truckers don't go on strike. Real supply chain problems magnified from what we have now.

 

[Gargoyle]

There are temperature sensitivity charts if you google. Whoever put the charts together assigned a coefficient to a list of powders. The lower the number assigned, the better temp insensitivity. I noticed the temperature of the round, or powder inside the case, matters a great deal. If you are shooting on a cold day, with ammo matching the same temp, the lower the velocity. Conversely, keep the rounds warm in a pocket next to your body while shooting on that cold day and velocity stays higher.

If I am stuck load developing in the winter for rounds I am going to shoot mainly in the summer with 100F temps, I'll try to keep the rounds as warm as possible to check for high pressure signs.

 

[Alexander-M]

Timely thread. I had been wondering the effect of temperature on H4831 or H4831SC. I had data of muzzle speeds as measured with a Labradar at 80° and 40° temperatures, but I wanted some data a bit colder.

Fortunately, this past week we had some cold days, and I used the opportunity to add to my data. On Wednesday 26 January 2022, I shot at the BRRC in Wright City, where I normally shoot, and where I collected all the data. After setting up the ShotMarker target, the LabRAdar, and other gear, I started shooting at 7:45 am, and shot until 8:30 am. The temperature remained at 0°F throughout this interval according to the thermometer in my 2018 Nissan Murano, and according to one other person’ car who was in the Club office at the time.

I understand this is limited data, and since I did not record the relative humidity, the air density is unknown. Still, I believe the data provides an indication of the trend.

Here is what I recorded:

Alex