Temperature Sensitivity with IMR 4831

N

Natty270

Inactive
I started reloading for hunting and have a couple rounds worked up for my 243 and 270 using IMR 4831. I had good success last hunting season as my hand loads resulted in 5 dead deer in Southwestern Wisconsin. 4 with the 270 and one with the 243.

I have read about IMR4831 being temperature sensitive. I worked up the loads in mid April 2019, and just wonder if I need to be concerned about IMR4831 and temperature sensitivity.

I believe the coldest day of the 2019 gun deer season in southwestern Wisconsin was the first day 19 degrees. The rest of the season was pretty mild. From time to time we have some pretty cold sits in the ridgy hardwoods.

What kind of issues arise from powders being "temperature sensitive".

I worked up a load for each rifle with H4831sc (270), and H4350 (243) that both shoot sub moa. Just wondering if I should stick to the Hodgdon?
 
Normally, when someone talks about a powder being "temperature sensitive" they are talking about cold. Cold temps slow the speed of (most) chemical reactions. Just as they affect the function of batteries (also a chemical reaction).

What normally happens is that in very cold temps the powder charge produces LESS pressure and therefore lower velocity.

The important question is "how much?"

I don't know of a formula for that, but there could be one. What I do know is that with many rounds, if you lose 100fps or so, you get about 1/2" more drop at 100yds.

If you have a chronograph and the nerve to face the cold, you could test your rifle and loads at different temps and see just what difference there is.

The old rule of thumb was always work up your max loads in summer heat, and they will be safe (and slightly less powerful) in arctic cold.

Doing the opposite might cause problems.

Expect your rifle to hit a little lower in sub freezing temps than it does at 70 degrees. How much, you'll have to test to find out. Might not be enough to matter, or might be important, depending on what you're hunting, and what ranges.
 
QuickLOAD has a temperature compensation calculation feature for powders that don't feature temperature compensation coatings.
 
Both of the Hodgdon powders you referenced are temperature insensitive.
I believe that both H4831SC and H4350 will change about 12 to 8 fps respectively from 0 to 125 degrees F.
(That is from memory and my memory isn't all that great anymore.)

Varget changes 4 fps and H4895 changes 8 fps over the same range based on data for .308s. Those measurements I am sure are right because I use them all the time.

The changes in velocity aren't perfectly linear across the 125 degree range of temperatures but the changes are linear enough to make an estimate that would stay within any set of measurements with a chronograph.

It is pretty easy to calculate the velocity change for each type of powder.
There is some data on powder comparisons on Hodgdon's EXtreme Powder web site. It is very spotty so your particular powder might not be included in any of the comparisons.

By comparison, I believe that IMR4350 changes about 155 fps from 0 to 125 degrees F. That's 1.24 fps per deg. F. compared to 0.064 fps per deg F. for a powder that has an 8 fps per 125 deg. F. range. Also, from the Hodgdon data, it appears that the velocity change over the temperature range is somewhat dependent on caliber. Some of the .223s sensitivity seems to be larger than that for the .308s for the few powders that were listed in both calibers.

I believe most IMR powders fall in the 120 to 155 fps range over 125 deg. F. for the larger calibers. (Again that is from memory but I believe that those numbers are pretty representative.)

I believe that the only IMR powders that are temperature insensitive are the new Enduron powders. IMR4166 Enduron and IMR4451 Enduron are both temperature insensitive. I have used both and they change about 20 fps over the 125 degree range.
 
Thanks for the additional info on this thread. Good to know. I plan on testing these rounds on a cold day soon. I'm guessing I should put the rounds outside and let them get as cold as they would if I were hunting all day.

There is definitely more to this hand loading than I ever thought there was. I think that is what I enjoy the most.

I've been passing the knowledge to the boys in camp and we are all better shooters than we used to be, that's for sure.

Thanks again
 
I shoot a lot in the cold--it's amazing how much velocity loss I sometimes see, though some of that is attributable to denser air when cold/dry (which arctic air masses typically are).
 
The other consdieri is how hot are your loads?

If you have maxed them at cold or cooler temps then it can push you over the edge if you are target shooting at 80 (not saying it will, just can)

If its a bit over mid load, very unlikely.

Worst then is it might take you out of the sweet spot for the barrel harmonic and group opens up.

Not likely to be enough to be a hunting factor if you are 1 MOA area with the IMR.
 
That's good info and duly noted:

Funny you mention hot loads.

I found out that the 58 grains of IMR 4831 I'm using on the .270 130 gr Hornady interlocks is above max by 2.2 grains. The data I used is from the Hornady 4th edition manual that was given to me, and the speer #10 manual. I did not know that powder changed over the years. The rounds are only for hunting so would only be used in cooler temps anyway, but they are hot. I worked up the loads in April of 2019. They are accurate as heck but i'm now wondering if I should be concerned shooting that over max load out of my rifle?

I just re-checked the primers for pressure and did find they are pretty flat, but no bulging or enlarged primer pockets or cratering. They did a heck of a job on whitetail, but I do have a couple other loads that were almost as accurate.. 54.4 gr of IMR4831 looks like a 1.25 moa., 55.8 was 1 5/8. 58 gr was 1.0 moa.

I was thinking about pulling the bullets as I have loaded quite a few of loaded up already. Any addition input is certainly helpful.
 
Old manuals often have data developed by watching for pressure signs in a production firearm and never checked for pressure in a SAAMI standard pressure and velocity test barrel. As a result, the pressure might have been fine in their production gun, but not be fine in yours. My old Hornady #2 is like that. I don't have a copy of #4, so I don't know when they changed over to actually measuring their maximum load pressures, but I know they have. I believe everyone does that now for liability reasons.
 
Temperature sensitive powders might make a difference to a 1000 Yard target shooter. For shots at deer out to 300 yards you ain't gonna know the difference.
 
pete2 said:
Temperature sensitive powders might make a difference to a 1000 Yard target shooter. For shots at deer out to 300 yards you ain't gonna know the difference.
Click to expand...
You might. Zero the wrong powder in on a 90 degree day you will miss a deer on a 10 degree day.
It actually does not matter as much to a target shooter as it does a hunter.
 
I have since switched to H4831 for my 270 WIN as my go-to powder with the same great accuracy. The powder is more temp sensitive, but is not as critical in a mid-range stock hunting rig. At the same time - every little bit counts.
Click to expand...

H4831 should be less sensitive not more. Not sure how far back you have to go but the last (8?) at least is less sensitive.

If you list your gr you are using we can cross check the various manuals to see where you are at.

Other pressure signs are marks on the back of the shell base and if the bolt is sticky. Any one of those is cause to back off.

As for accuracy, as long as you are 1.5 inch at 100, you are good to any reasonable range. If its 100 yds limit then 2-4 works (that is all ball park). At 200 that gives you 4 to 8 inches and that is getting iffy.

Barrels have sweet spots and you never know where that will be. If it shoots that well at max loads, then there should be other nodes below that which are as good so its worth testing.
 
I've done all my load workup in colder weather, but I'm just starting a new workup as I found out the load data in my Hornady 4th edition manual is outdated resulting in me loading a bunch of rounds over max for both my 243 and 270. I decided to pull these bullets and start over with IMR4831, H4350 (what I have left), and RL-19. I also have worked up loads already for the 270 with H4831 that shoot well, but in the new Hornady 10th edition book they show under 2800 fps (which doesn't really bother me). My most accurate loads with IMR was almost two grain over max in the new book, and my 243 load was over max with H4350. Live and learn. So after I rework some rounds, my goal it to have go to recipes in multiple different powders between 2800 and 2900. Again, these rounds are just for hunting. I just worked up some 58 gr Vmax and 75 gr Vmax for the 243 and had excellent results with both in lower FPS. Now I need that coyote that lives behind my house to slip up!!

Thanks for the responses!
 
For those who may be interested.

For those who may be interested. The following data is the max load from Every Hornady manual for the .270 win. 130 gr. bullet with 4831. One caveat. Some early manual numbers may be with the slower milsurp 4831* sold by Hodgden.

#1. 61.0 gr.*
#2. 61.0 gr.*
#3. 57.1 gr.
#4. 57.2 gr. H4831 59.6 Showed data for both versions.
#5. 56.1 gr. H4831 62.0 gr.
#6. 56.1 gr. H4831 62.0 gr.
#7. 56.1 gr. H4831 62.0 gr.
#8. 56.1 gr. H4831 62.0 gr.
#9. 56.1 gr. H4831 62.0 gr.
#10 56.1 gr. H4831 62.0 gr.

Loads #1 and # 2 I believe are definitely the old milsurp 4831 sold by Hodgden.

Load #3 is probably the first lot made by IMR (Du Pont)

Loads #4 through 10 as made by IMR. The 4831 by Hodgden might be their first batch made in Scotland to duplicate the original milsurp. (my best guess)

Loads 5 through 10 are, again my best guess the powder made by ADI in Australia for Hodgden.

Considering the no change in charges for either the IMR or H versions, I'm guessing the loads have not been retested for some time.

There are manual that in the past have not state whether a particular powder like 4831, or 450 for that matter was by DuPont (early manual) or IMR or H which adds to the confusion, especially for new reloaders that happen to have older manuals.

Dunno if this helps to clarify anything but here it is FWIW.
Paul B.
 
Thanks for putting that up. It's a good lesson in how data and powder can change over time.

I read that Hodgdon upgraded their QC system around 2000, tightening burn rate specs and test requirements. I think the results of testing done after they tightened the specifications probably changes very little if at all.

It is also the case they don't use the SAAMI spec quite the same way commercial ammunition manufacturers do. I should write it up for a separate post, but the bottom line is their loads have a little bit more safety factor in them, for the most part, than SAAMI strictly allows.
 
reynolds357 said:
You might. Zero the wrong powder in on a 90 degree day you will miss a deer on a 10 degree day...
Click to expand...

Probably not.

Delta 80° - worst case, call it 100 fps.

If you take the fairly std. load of .270 WIN/150 gr. NP/2800 fps-MV, from a scoped rifle, and sight it in for 25 yds., which is MPBR (+/- 3")?

... the drop at 300 yds is (-5.3").


If, however, you lose 100 fps to powder temp sensitivity, and that MV drops from 2800 to 2700 fps?

... the bullet drop at 300 yds becomes (-6.9").

A hair over an inch-and-a-half, at 300.

And, if you expected it, a shade of "Kentucky Elevation" would compensate for it.




Red
 
With constant barometric pressure, I get a total drop difference of 2.4" at 300. The reason is the cold air is denser, so you have extra drag from that on top of the lower muzzle velocity. Nonetheless, it's not outside the kill zone of a deer.
 
Delta 80° - worst case, call it 100 fps.
Click to expand...

Depends on the powder. MOST powders will vary anywhere between 1 fps to 3 fps for each one degree of temperature change. It could be closer to 250 fps than 100 fps. You'd just have to do some individual testing with your rifle and load to know for sure.

Most of the powders formulated to be resistant to temperature changes will still vary, but will be closer to 1/2 fps for every one degree of temperature change. That would be only about 40 fps loss with 80 degrees of temperature change.

But 80 degrees temp change would be pretty rare. Most load manuals give data at about 70 degrees so going down to 10 would only be a 60 degree change. And if you live/hunt in a colder climate you'd probably be working up loads at temps lower than 70 anyway. If you can keep the temperature where you did your testing within 40-50 degrees of where you're actually shooting it isn't terribly hard to work with.

You can still make common powder work over a wide range of temps. It's just one less variable to mess with to use the more resistant powder.
 
QuickLOAD has a fairly sophisticated temperature model, and it put the drop for 4831 at -99 fps for that 80 degree drop from 90. I'd have to check, but suspect it's a nonlinearity that is responsible.
 
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