Temp differences and MV

[ndking1126]

I've gotten into handloading and have picked up a really accurate rifle. Having the accurate rifle has raised my confidence in my shooting ability since good, consistent groups are becoming the norm.

I have long suffered from inconsistent and wandering groups with my hunting rifle though. So one answer is to start loading for it also.

I live in the south where it gets really hot most of the year and hunting temps can be anywhere from 20-55*.

In an effort to remove one more variable, I'd like to test ammo at different temps, but on the same day with the same setup, and me shooting the same. (Maybe in June I shot well, but in Oct the groups aren't so good and I'm not sure if it's the change in temp or me messing up.)

Is there a way to test this without waiting for winter to get here? For example, load up 10 rounds and then refrigerate 5? If I could shoot the 5 while they are still around 40*, would that accurately replicate the winter conditions? As I see it, I would attach my magnetospeed, pull a round from the cooler, chamber it, and then fire right away so the chamber couldn't change the overall temp of the round. If the velocities of the 5 refrigerated where basically the same as the 5 that were at ambient temps (probably 80*+), I would have a reasonable belief I could practice now and still use the same round later in the year.

I've been doing a lot of reading on the fact that temp affects velocities, but very little on how to work with it, other than just waiting for winter to get here. Thanks!

[ndking1126]

One other thing.. I really like the 10 shot ladder test that can be found on the website. I intend to proceed with that process, but I guess I'm looking for a way to validate the results, not just assume that the bullets will still be accurate and at a similar velocity.

[jmr40]

It depends on the powder you use. Some are more sensitive than others and you can see 1.5-3 fps velocity change for every 1 degree temperature changes. Others are specifically designed to be resistant to change. Those will typically only see 1/2 fps velocity change for every 1 degree temperature changes.

The numbers you see listed in ballistic charts are usually at about 70 degrees. You'd have to see a loss of close to 100 fps to be noticeable at typical hunting ranges.

All things being equal I tend to choose powders that are not effected by temperature changes. The "Normal" temps that I hunt in range from 20-50, but I've hunted in temps in the single digits and as hot as the upper 90's. But by choosing the more stable powders I won't see velocity change enough in those ranges to matter.

[ndking1126]

Thank you for the input. I've started working with h4350 as I am told that's one of the ones that are not affected as much. Would you agree?

I consider the shots I will take are normal. I'm not going to shoot more than 350 yards with good conditions. I killed an antelope at 330 a few years back, so I know I can do it when conditions and equipment are right.

When I killed the antelope I was pretty confident in my shooting ability, but I didn't know as much as I thought I did. Now that I am hand loading, it opens up a lot more variables and I'm enjoying learning.

[Rimfire5]

The Aberdeen Proving Grounds published an article testing .308 military ammo in temperature ranges from 25.5 deg. F. to 130.5 deg. F and noted that the overall rate change in temperature was 1.7 fps per degree F. across that range. However, the majority of the change occurred above 100 deg. F.
I used the data in a temperature range from 30 deg. F. to 110 deg. F. (+/- 40 deg. around a 70 deg. median) for their data. I then used QuickLOAD to
calculate the effect of temperature for 30 deg and 110 degrees around the QuickLOAD 70 deg F. default value for powders that I use to calculate the # fps per degree F. for each powder. I performed the calculation for each of the calibers that I use the powders for.

Here is data that I amassed from QuickLOAD for powders and calibers I use most.
The article referenced was from Aberdeen proving grounds.
The QuickLOAD data seems to show sensitivities by brass size(powder load) but the sensitivity seems reversed for VV N140 powder for 6.5mm CM.

    Powder   Overall  .308   6.5mm CM  .223 Loads
Article      
 Military    1.38      1.38	
QuickLOAD	 
  IMR4895    1.39      1.26               1.53
  H4895      1.12      1.16     0.79      1.41
  IMR4064    1.00      1.19     0.81	 
  IMR4166    1.18      1.28     0.98	 
  IMR4451    1.04               1.04	 
  IMR4350    1.15               1.15	 
  Varget     1.13      1.20     0.84      1.36
  N140       0.93      0.95     0.61      1.23
  RL-15      1.29      1.29	 	
  CFE223     1.56      1.43               1.70

[Unclenick]

Ndking1126,

Read this article.


Rimfire5,

No idea what your table is supposed to signify since there are no explanatory headings or units. Are you trying to show something about temperature effects (the subject of this thread)? I can't tell.

Put everything inside code tags ([code]*content*[/code]) so leading spaces will work, and then you can organize columns. The code tags will create a little window that readers can scroll through to see the data, but we need labels or an explanation of what those numbers signify.


All modern smokeless small arms powders sold today use a nitrocellulose base or a nitrocellulose and nitroglycerin combination base, and Vihtavuori is no exception. Burning characteristics among stick powders are controlled primarily by base deterrence and grain geometry.

QuickLOAD's instructions tell you the temperature compensation entry button is valid only for powders that are not temperature compensated if you are trying to show something about that.

[Rimfire5]

Unclenick,
Thanks for the guidance on code tags. I'll use that in the future.

I was attempting to show the relative delta in fps per degree between powders at 30 degrees and 110 degrees for each powder and for the different calibers. I had mentioned that the article referenced was from Aberdeen Proving Grounds in their test of Military .308 rounds in the temperature range of 25.5 to 130.5 degrees. I used 30 to 110 degrees for my data because that is what we would normally experience in Northern VA.

Somehow in the middle of the post I lost the screen after entering a relatively long sentence about the process. When I got the screen back the explanation apparently was lost and I didn't notice it in my efforts to create columns that could be read.
I'll be glad to edit my post to add the explanation that somehow got lost.

I take it you expected to see numbers for each temperature rather than the delta effect in fps across the stated range of temperatures.
Maybe I consolidated too much data in an effort to keep the post short.

[Unclenick]

I went ahead and put them in. If you go back and edit the text with leading spaces to line the columns up, it will work now.

I didn't know it was Δfps, so the edit is a big improvement.

Realize that if you used QuickLOAD's temperature entry, the results for H4895 and Varget and the Enduron 4166 and 4451 powders will be wrong, per QuickLOAD's instructions, because they are all temperature-compensated powders and don't match the temperature effect function in QuickLOAD.

[Rimfire5]

I guess I will be using the chronograph to see if I can dope out the effect of temperature on those powders.

I load for 'exit time' to keep the shock wave from the powder ignition at the chamber when the bullet is exiting the muzzle so knowing the impact of temperature on velocity is an important aspect in determining the exit time.
If I can't count on QuickLOAD for those powders, it makes things a bit more complicated, especially since IMR4166 is my most accurate .308 powder and IMR4451 is my most accurate 6.5mm CM powder.

During the cold weather in December, using the temperature adjustment in QuickLOAD seemed to keep the accuracy gains using exit time in the right ball park for IMR4166 and IMR4451 powders on days when temps were 40 degrees or more below the QuickLOAD 70 degree default.
When I don't use the temp correction on cold days, the accuracy drops off as if the muzzle velocity had dropped more than 40 fps.

[Unclenick]

It gets messier than that. Check out the temperature testing in the article I linked to in Post #6. Your testing may, indeed, be the best approach. One of the points that comes up repeatedly is the temperature compensation seems to work better in some chamberings than in others.

[Rimfire5]

Thanks for the heads up.
This weekend will be especially cold in NVA so it should be a good test.
I have some IMR4166 loaded for my .308 and ready to test.

I did look at the article and saved it as a reference.

I hope the table is now readable, even it some of the QuickLOAD data on some of the powders may be questionable.

[Rimfire5]

Unclenick,

The article cites that primer types, barrel temperature, and powder temperature can be variables when considering the results of temperature change and that all three need to be considered. I was quite impressed with the article and found that the author's findings agree with observations made during my less formal experiments.

Without having read his initial suggestions, I realized quite some time ago that I needed to keep the variables he cites as constant as I could in order to focus on the outside temperature variations when shooting for accuracy.

1) In my approach to achieve accuracy with my most accurate rifles and attempting to keep the bullet exit time to match the reflection time of the barrel steel, I always use the same primers for each caliber (choosing primers based on testing of different primers with the same loads to determine which yields the best accuracy). The primers are not a variable. 1a) By the way, I have tested using magnum primers versus regular primers on my .30-06 hunting rifles in 23 degree cold temperatures and measured a 12 fps increase with the magnum primers versus regular primers using my chronograph. I think that is in the range of increase that the article indicates. It isn't enormous but there is a slight increase.

2) I have temperature strips (86 to 140 deg. F.) on my all match rifle barrels and monitor barrel temperature when shooting groups to ensure that the barrel temperature doesn't climb more than 5 degrees for any group. I also have documented that my best rifles' POIs drop by between 0.25 and 0.35 inches depending on the caliber when temperatures of the barrels climb to around 122 degrees. I generally stop shooting and allow the barrels to cool at 110 degrees before the POI drops and then start my groups over at 86 degrees. Once I start shooting a group, I don't waste time letting a cartridge get hot sitting in a hot barrel, as the author recommends.

3) My results with Hodgdon's 'Extreme Powders' (particularly H4895, IMR4166 and IMR4451), like the author observes, indicates that the velocity does appear to change with temperature regardless of what Hodgdon claims. I had thought that the adjustments I was making using QuickLOAD to match temperature forecasts were working because I was getting group average results at 35 degrees that were as good or better than the results I was seeing at 70 degrees early this Fall with charges matched for that temperature. Of course the powder charges were slightly smaller in the warmer temperature, sometimes by tenths of a grain. What I have determined is that all these powders are lightly less temperature sensitive to changes below 70 degrees than they appear to be at temperatures above 70 degrees. The curves aren't perfectly linear but are near enough to consider them linear. Aberdeen Proving Grounds data also shows the velocity changes are not quite linear.

4) I had also noted in the table that the smaller calibers seem to be more sensitive to temperature. The author also makes that observation.

You picked an excellent article to reference. It is a keeper.

[zeke]

ndking1126-All the studies done on temp change are really useful, but like the computerized drop tables, may need to be checked in the field. Used to hunt up here, when 20-30 degrees is considered out of the ordinary warm. Worked up hunting loads at same time of the year, but have a range within 5 minutes. Other possible considerations are difference in clothing between seasons, testing with same rifle hold (forearm grip) and shooting position.

[ndking1126]

Unclenick, thank you for the article! A quick glance seems to be exactly what I was asking about. I'll read it more in-depth a little later today. I'm happy to my own "experiments" also, but with limited time to get to the range, I always prefer to be as prepared as possible.

If anyone else has some input, I'd love to hear it. Zeke, I think the variables you mention are really the heart of my question. I'd like to remove all of them by shooting both hot and cold rounds during the same range trip. I'm not concerned with external ballistics with this, just the change in muzzle velocity.

[ndking1126]

What I took away from that article is that taking cold/refrigerated rounds to the range and firing them in the summer is not in a completely accurate replication of shooting in cold weather because of the change in barrel temp. He specifically found that the barrel temp was a bigger factor than the powder temp. Having said that, I don't think it would be a waste of time because the variables of temperatures would at least be CLOSER to the desired conditions and would give me somewhat of an idea.

If I did it in the winter and shot rounds that had been heated up to about 80*, that would be probably even closer still. First, shoot the cold rounds with a cold barrel. Next since the barrel has heated up, go get the rounds out of the car that are still warm and shoot them.

That would duplicate both rounds and barrel being cold, and then both rounds and barrel being warm. Without all his gadgetry I wouldn't have any way to determine if the barrel temps were 65, 85, or 125.. all I would know is that it would be warmer.

Seems like a start.. I guess I need to get to range before it gets too warm! Haha, thanks again Unclenick.

[Unclenick]

It depends what you are trying to prepare for. If it is cold weather match shooting, then replicating the pace of the match will tell you how your POI is affected by the temperature and any fouling you accumulate during the match. If you are planning for hunting, I like to suggest cleaning the barrel and shooting three shots onto three targets rapidly enough to simulate a clean cold barrel shot with two follow-ups. Clean and cool the barrel and repeat. When you've accumulated enough shots to distinguish any change in POI between them, you have an allowance you can make for the shift.

[ndking1126]

Mostly I just want to shoot consistently small groups when I go to the range. I did start hunting again this year and seem to have found an opportunity that I can take advantage of year after year so that would be the most practical application.

I've wanted to compete, but never have. That's due to a lack of time more than anything, but now that I'm really starting to get things figured out, I'm thinking more and more that I should give it a go.

I think this turned into a pretty informative post.. Rimfire,
Knowing that's the change of fps makes sense. I couldn't figure out what it was saying. Your 4 points are informative, though. Thank you for your input!

[hounddawg]

120 gn SMK 43.5 H4350 developed in mid 70's weather, had to come up .5 MOA yesterday in low to mid 30's yesterday. The load was dead center last December when I was developing it and the scope was not touched before last week. Had to come up 1 MOA when temp was in the mid 40's and another half MOA yesterday at 34F. Using the JBM calculator when I got home it said I had dropped 75 FPS from the mid 70's to low 30's

One thing I do know is increasing a charge in a load the speed is never linear, why would temperature be linear? I have had charges remain flat for .4 to .5 gn increases then suddenly jump 50 to 75 FPS by increasing .1 more so why would temp be any different

[Unclenick]

Hounddawg,

What range were you measuring the drop at?

That big a jump is concerning. It indicates an increase in pressure due to increased burn rate or due to something loose that has been stretching that is coming to a stop, like a bolt lug that wasn't making good contact until that last little extra bit of powder went in.

[Rimfire5]

I would have thought that the drop in POI that hounddawg experienced indicates a drop in pressure and velocity not an increase.
What am I missing?

Based upon the Hodgdon data on H4350, I wouldn't have expected a significant a velocity change. If it was IMR4350 I would have expected it.

I shot IMR4166 (also an extreme powder) at 25 degrees to 30 degrees yesterday and didn't seem much change in POI after the barrel got to around 80 degrees.
I never left a round in the chamber longer than about 5 seconds, so according to the article you provided, the cartridge temperature didn't rise more than 1.25 degrees (1/4 degree per second). The temperature of the rounds sitting on the bench for a 2 hour period were in the 25 to 30 degree outside temperature range.

But before the barrel warmed up to around 80 degrees, I noticed that the POI wasn't as consistent. I can't explain that. But maybe it was me getting used to the heavy layers of clothing that I needed to keep warm.

I never let the barrel get hotter than 95 degrees and then let the barrel cool to 86 before shooting the next group. Once I did that, the POI was right on for two different loads.

[hounddawg]

@Unclenick, load was the rough load development at 100 yards back in mid December in mid 70's. Last Monday or Tuesday I did a sight in at 600 when it was in mid 40's then the match yesterday started at 8 am at around 30F increasing to low 40's by afternoon. I wasn't expecting much from the load but ended up at a solid 96% with only one flyer in the 8 ring that was my fault for shifting my weight with my finger on the trigger otherwise it was a pretty solid load considering the development, some mild wind conditions and mirage. Yes Virginia you can have mirage in cold weather. I looked through a Celestron sighting scope set at 60 power and it looked like a pinwheel, at 24 power through my rifle scope it was milder but visable

here is the thread for the original load workup back in December

https://thefiringline.com/forums/sho...d.php?t=599693

[zeke]

The range at which the drop is measured can matter significantly, remembering bullets travel in an arc trajectory. At 600 yds, likely the bullet is already dropping. More of a drop may be related to a decrease in velocity. One of the common trajectory (come up) programs is very useful for checking this. If the increased "drop" is at an earlier part of the trajectory where the bullet is still climbing or level, the increased "drop" may be indicative of an increase in velocity.

Most of my rifles are sighted in at 100 yds. If the bullet starts impacting noticeably lower at 100 yds, one of the first things (and there are others) that may be occurring is an increase of pressure / velocity. As in the bullet may be leaving the barrel earlier in it's rising recoil.

Course it is just an opinion of what i would be checking for my own purposes.

[hounddawg]

I would have thought that the drop in POI that hounddawg experienced indicates a drop in pressure and velocity not an increase.

yep it was a decrease

Based upon the Hodgdon data on H4350, I wouldn't have expected a significant a velocity change. If it was IMR4350 I would have expected it

that's what I would have thought also. If you look at the original load workup there was an increase of about 6 to 20 FPS every three tenths of a grain, but the numbers are what they are. In retrospect I should have bumped my charge up a tenth or two, I had decent groups as far as my CEP numbers went but the groups were not as tight as I would have liked and my X count was low. I think a load bump up would have helped that

Like I say I am just learning this stuff and trying to figure it out myself. It helps throwing it out here and getting opinions on the why's

[Rimfire5]

zeke,
I didn't think about the bullet leaving the barrel earlier in the recoil cycle if it was at a higher velocity.
That could explain the rise in PIO.

[44 AMP]

I have long suffered from inconsistent and wandering groups with my hunting rifle though.

A lot of hunting rifles aren't made to shoot good groups. They're made to put one, or two, possibly 3 shots at or close to the point of aim, and after that, not so much. If shots 3-5 are within a few inches of 1-2, that's usually minute of deer, and good enough under usual field conditions.

Varmint and match rifles are much different creatures than the usual deer rifles.

There are a couple of things I didn't see touched on enough talking about the idea of shooting chilled ammo to replicate cold hunting conditions on a warm day. First, one that was mentioned is wearing those same cold weather clothes or not. Wearing your cold weather hunting gear vs. a t-shirt at 79F DOES affect your shooting.
Another point, is the temp of the RIFLE. Everything behaves just a little differently in the cold than the heat. Some things behave a lot differently.

20F is enough below freezing to qualify as cold, in my book, but its not the same as sub-zero temps, and I have hunted in both. Likewise, when its 110F in the shade and there is no shade, things act differently.

Long standing rule is to work up your top loads in the summer, and you will be safe in the winter. The reverse may not be true.

A one of things I learned as a youth in deer camp in the middle of an Adirondack winter was that when there was a nice warm cabin at the end of the day, the guys that knew what they were doing left their rifles and ammo outside!