yeah Mate I hear you with that last bit...if it works and works well DONT F$#% WITH IT........go with it and be happy

Hey Slim..... thought of you when I seen this !!!

Tempreture Test

Scroll to bottom of page you'll find a chart.
The results are not as predictable as one would think. Especially IMR4064 and Varget.

Ok, chambered, I thought Varget and 4064 did pretty well. Plus most of these powders did much better than some of the ones I tested.

Description that goes with the chart "Data based upon the 308 Win. cartridge using all the same lot number Winchester cases, Winchester Large Rifle Primers and Sierra 168 gr. BTHP Match bullets. Note that many ball powders can exhibit unexpected extreme changes in pressure below 35 degrees F and above 105 degrees F, rising pressures 10,000 psi or more at elevated temperatures. Be careful at the temperature extremes! In addition do not use ball powders at very low load densities.

Data courtesy of Varget."

this shows that what is said about the ADI powders is correct, the stick types are less sensitive.

This is just one example. A powder's sensitivity will change with different bullets and calibers, e.g., Varget isn't always this great. There are plenty of stick powders that are sensitive to temperature.

My point was the results don’t show what is most commonly believed !!!
(Temps drop pressure drops…temps rise pressure will rise)

1) 3 of the 7 powders had an increase in pressure when the temperature dropped.
2) 3 of them had a pressure drop when temp increased.
3) IMR4064 and Varget had velocity increase on the hot temp even though there was a pressure decrease.
4) 2520 and 4064 had a decrease in velocity even though the pressure increased with the dropped temp.

gotcha, I have experienced some velocity increases with temperature decrease. Their sample size was not annotated but I don't believe Varget velocities within 7 or 8 fps are statistically significant. IMR4064 probably is.

Thanks for sharing. I'm sensitive to this right now and am developing my loads after they have sat on ice so I can get the powder temps down to the mid-30s.

I never did any extreme temperature testing with Varget but I can tell you this.
When I was load testing for my 7mm08 I ran a lot of rounds over the chronograph and it was amazing to see how consistent this powder can be.
If I remember correctly the worst loads deviated about 20 fps. The best was a 10 shot string with an extreme spread of only 7 fps. That was done in a manner that kept the barrel from getting to hot too quick.

With the right cartridge and bullet combination IMHO it's simply one of the best !!!

I wish Varget was better suited for the 6.8mm SPC.

Always use caution when using double based powders (ball powders) below -30 degrees. At extremely low temperatures the nitroglycerin in double base powders will detonate causing damage to the gun and shooter. Not many folks are likely to be hunting in temps below -30 but if you are one of the few keep your cartridges in your pocket and not in the gun at extremely low temps.

This whole subject of temperature effects has piqued my inquisitive nature and I have been reading lots of blogs, articles and posts. Like SlimJim I prefer empirical data to anecdotal but people's experiences can point to areas of enquiry. That is how I started thinking about how the temperature of the rifle may also affect velocity of the bullet. I have found only one good article on this and I share it below.

www.shootingsoftware.c...actors.pdf

MacD, this is a good article and I have studied it as part of my temperature sensitivity journey. I tried to determine the affects of barrel temperature on muzzle velocity in several tests. Its not a first order or even second order contributor unless the heat/cold of the gun is changing the powder temperature. Besides the rapid fire tests below, I have also looked for trends in my data looking for a small increase in the velocity of subsequent rounds - I have not found any evidence of it with the powder, bullets, and rifles I have used. That doesn't mean I'm saying it doesn't happen. Every bullet/powder combination has its own traits, e.g., same powder in a different cartridge and bullet weight can behave differently to temperature changes. Most of the heat generation is at the muzzle not the breech in the testing I have done. (Note, I'm not about to take my prized .270 and subject it to the abuse of a multi-shot rapid-fire test).

I did some more testing this weekend and will post results when I get them compiled. I've been very pleased with the results this summer of developing my loads with cold rounds (chilled on ice). I have much more confidence going into this hunting season.

I’ve done these temperature sensitivity tests multiple times now. These three powders have been pretty consistent in their performance with the 6.8mm SPC. AA2200 is losing are 9 fps per 10 degree drop in temperature. 1200R continues to show the worst temperature sensitivity and lack of consistency which is why I have stopped using it (don’t load this powder near max and go out in warm weather). H322 has shown itself insensitivity to temperature change but does not have the energy potential of the other two powders, at least in warmer weather. In colder weather, the energy difference between AA2200 and H322 is not as significant as was shown in the prior graph of velocity vs powder charge vs temperature. I’ve also noted that there must be other factors in play here because sometimes a muzzle velocity at 25 deg F will be higher than 45 deg F with the exact same load but on a different day. That is why it’s important to look at and compare test results done on the same day/range session.

Before you start thinking that H322 will do wonders, changing the bullet and or changing the powder charge (even with the same powder), can yield different performance. So will using the powder in a different cartridge or case. Below shows the difference between the 6.8mm 100gr AB (center insert) with the 110 BTHP. The temperature sensitivity of the two loads were similar but the lighter 100 AB bullet with a higher powder charge didn’t maintain its POI as well as the 110 BTHP, both with H322. The 100 AB group in the middle was from the prior range session at about 80F. It was my first good grouping with the 100 AB on top of H322 and was achieved by just a COAL change (changing powder charge was not working). This 100 AB load is longer than mag length (2.370") which allows for more powder capacity and above average velocity for a 6.8mm.

Note that every rifle is different and yours may better or worse results than seen here. You won’t know until you test in both summer and winter conditions. It hasn’t been that difficult to test for cold temps during the summer. Throw a bag of ice in a cooler with your cartridges laying on top, wait 45-minutes, and your powder temperatures will get down into the mid-thirties (page 6). I plan on continuing to do my load development using this process as I believe it yields more reliable results for the hunting season ahead. The ultimate proof will come with actual shooting and hunting in cold temperatures. At least I don't expect to be surprise as much as I was last hunting season with my 1200R loads I had worked so hard to develop.