I've been interested in how various powders perform over temperature. In the past, I have not achieved the near independence from temperature that Hodgdon advertises. However, I guess I have to change my tune--in some cases, the Hodgdon powders do better than the others (but not always).

Last winter I ran a bunch of loads through the chronograph when the weather was cold. Some of the data was taken at 24 degrees F, and some at 45 degrees F. Today, we had sunny, hot weather, so I headed out into the desert and shot rounds from the same load batches again.

I've run the data through regression in Minitab. This conveniently gives upper and lower confidence limits on your estimate. So when you look at the numbers, you see a 'low' number, an 'estimate', and a 'high' number. Statistically, the 'estimate' is the best estimate of the feet per second per degree F. However, since this is an estimate, we have to put some 'siderails' on it to indicate how much error might be associated with 'estimate'.

Rounds were fired from a 20" Browning .223, a 29" Swedish 6.5x55, a 22" Howa .308, and a Browning 20" 30-06.

In each case, .223 Winchester 'military' ammo was fired, to provide a check on the chronograph. In all cases, the .223 velocities were as expected. This indicates that the chronograph worked consistently.

These are the resulting 'slopes', i.e., the shift in feet per second per degree F.

low estimate high
223, 24.1 grns H322 -.72 -.045 .63
223, 25.4 grns Varget 1.09 1.48 1.87
223, Winchester 'mil' .45 .92 1.39
6.5, 43.5 grn H4350 .41 .67 .93
6.5, 43.5 grn AA4350 .96 1.22 1.47
308, 46 grn Varget -.37 -.11 .15
308, 45 grn AA2520 .80 1.04 1.28
30-06, 57.5 grn H4350 .15 .72 1.28
30-06, 59 grn AA4350 1.94 2.26 2.58

Hodgdon H322 turned in a score that you can't distinguish from zero in .223, but Winchester 'mil' ammo was more consistent that Varget in the same caliber. H4350 is reasonably stable in 6.5x55, but not enough to get me to switch from Accurate 4350, which is about $2.50 cheaper in this town. Varget does extremely well in the 308. Why is it so different from the 223 case?? In 30-06, H4350 has a much better temperature coefficient than AA4350. Note the big difference between AA4350 in the '06 vs. the 6.5mm. The data suggest that temperature coefficient for a given powder is not constant from caliber to caliber. Probably, the powder that shoots the same winter and summer in one cartridge will behave much differently in another. One question that is unanswered is how much each powder varies from lot to lot. In one case, I know I got very different results out of different jars of Varget.

Denton, Thanks for providing your findings. Appears to be supporting the notion that you have decided to try.

Do you suppose that if the powder manufactuers revealed those "secrets" that we would be shot after they told us ?

Best regards,
Alex

Denton,
Sierra ran a study on temp - vs - velocity for three calibers and used both ball powder as well as 4350. As I recall they found an average of 2 FPS/Degree F. I found this to be fairly close for most extruded powders and WW760 ball powders. For the slower ball powders such as H870 and Ramshot BigBoy, I found 2.8 FPS per Degree F to be closer to the truth.

I have some data I saved from last winter at temps between -1 F up to 38 F. I have been waiting for a chance to chronograph in warm weather to verify this. I am hoping for a nice day in the low seventies, with low wind to get a normal temp baseline. So far I haven't had any on a free weekend. I will let you know my findings as soon as I get a chance.

FWIW, H4831SC Extreme seems to drop quite a bit in the cold as well. I didn't record temps last summer, so I must wait for the next chance to determine its rate as well.

Scott

Scott...

Sounds like some interesting data. I'll be interested in seeing your results.

Curious here, are you measuring ambient temp or the actual temp of the ammo?

On a cold day they're about the same, but in open sun, the ammo can get a lot hotter than the ambient temp because of radiation off whatever they're sitting on.

I found Varget loads in .223 to go way off the mark in hot sun conditions.

------------------
PowderBurns Black Powder / Muzzle Loading Forum:

www.hotboards.com/plus/plus.mirage?who=powderburns

Denton,

I did get a chance to test my RamShot BigBoy loads today.

Back in January, I shot the following from my M96 6.5 X 55. I shortened the barrel to 28" on this rifle. It has an 11 deg target crown.

142 Sierra MatchKing (moly coated)
PMC Brass
53.5 Grains BigBoy
Rem 9 1/2M primers
OAL 3.16"

Temp 37 deg. F
Results were as follows:
Average FPS = 2702
E.S = 16
S.D. = 7

Today using the exact same components, the results were:

Temp 86 Deg F.
Average FPS = 2870
E.S. = 36
S.D. = 14

It looks like 3.5 FPS per degree. I kept the ammo and thermometer in the shade for 20 minutes before the test. (It gave me a chance to test the Black Hills 52 grain Match .223 ammo. 3390 FPS, E.S. 74, S.D. 30)

This 6.5 x 55 load is a bit too stiff for hot weather as I found the bolt lift to be ever so slightly sticky. The extraction was easy. If I were a U.K. long range shooter, I would bump it up another grain. Those guys load stiffer than we do in the USA.

I will test some of the other loads as soon as I moly coat some more bullets. I am curious how H4831SC compares to January data.

Scott

Scott--that's a pretty fierce temperature coefficient. If you want to email me the data, I'll run it through the grinder and put Confidence Intervals around the slope.

Powder--I was pretty careful to let the ammo normalize to ambient, and to keep it and the thermometer carefully shaded. On the other hand, when it's 95F, it does take a long time for your barrel to cool. I was rotating from rifle to rifle to give them all a chance to cool, and the barrels were still hotter than what I wanted.

Denton,

It sure is! I didn't wait for the barrel to cool. I was loading single shot. I closed the bolt and snapped right away. Since the S.D. and E.S. values were fairly good, I don't think I was heating the round up too much.
I will dig up the January tape and send you a Excel sheet with both sets of data. I believe H870 may fall in this slope as well.

I think I may have some cold 7 Mag. 870 data, if I can find it. If so, I may load up a fresh batch to include in our experiment.

I do have some 6.5 X 55 data with 870 that came up lower than quickload predicted on a 36 degree day. This was with 140 MatchKings. The amount low was almost exactly the amount low with BigBoy. I guess I will buy my last box of 140 MK's so I can verify its difference with H870. I thought I had purchased my last box of 140's.

Oh well for the sake of science...
Scott

[This message has been edited by Scott H (edited 06-25-2001).]

With todays powders and using reasonable handloads I see this as an exercise in futility for the most part, but interresting never the less...

the only place I know where temp comes into play in the hunting field is in the poorly designed 458 Win. wherein in it must be loaded hot to be effective and then under heated condition it sticks the bolts....

------------------
Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

It's important in a couple of situations--

Changes in muzzle velocity of 100 fps or so can cause enough shift in point of impact to annoy a bench rest shooter. It's not that it changes the drop, so much as it is that it changes the bullet's exit timing with respect to the motion of 'barrel whip'.

In an '06, it takes a grain and a half or two of powder to boost muzzle velocity 100 fps. Shooting a load that has a big shift with temperature can be like adding that much powder over the limit. It's a very good idea to know how much you have to allow for this effect to avoid excess pressure. In some loads, there is no worry. In others, there is a lot.