Hello All,

I have a question regarding the so called “temperature stable” or Hodgdon Extreme rifle powders. I have been using H4831 to work up a load using the 208 grain Hornady HPBT bullets. Sadly I don’t get many chances to get to the range and therefore I have a nasty gap in my data and this is what has led me to ask my question.

Last month I built up 4 loads using 51.0, 51.5, 52.0 and 52.5 grains of H4831 respectively I got average velocities of 2255, 2290, 2319 and 2356 FPS. The ambient temperature was 89 degrees and the humidity was 8%. A little back story on these loads, they were my first rifle loads and I only separated the bullets by weight, I did not weigh cases nor did I separate the bullets by differences in bearing surface length. Due to not doing these extra steps my smallest extreme spread was 80 FPS and the SD for all strings were around or above 25 FPS.

When I Came home and began building my next set of loads I separated the cases by weight, I also separated the bullets by bearing surface length and then again by weight. I then carefully weighed out powder charges of 53.0, 53.5, 54.0 and 54.5 grains of H4831. When I went to the range today I got some interestingly good but also not so good results. The average velocities for the strings were 2310, 2367, 2400 and 2421 FPS respectively, the extreme spread for these strings dropped to no more than 44 FPS and the SD was around 8 to 15 FPS for all of the strings. These were the good results. Was has me concerned or confused is the 46 FPS drop in velocity from my starting charge this week from my ending charge last month, aside from the differences in bullet and case separation and selection nothing else has changed with the load. The COAL is still the same length, the same cases were used and the primers were the same as well. The only other difference between the two sessions is the weather, during the range session today the ambient temperature was 60 degrees Fahrenheit and the humidity was 70%.

So my question is this, can a 30 degree drop in temperature have such a drastic effect on a temp stable powder to see 46 FPS drop in velocity despite a 0.5 grain increase in powder charge or do I simply need to throw away or otherwise disregard my earlier results due to the lack of attention to detail when I built the earlier loads. Thank you in advance for your help and advice on this question.

Erick.

what are you shootin?
I had an issue while working up a ladder load on a 243AI at about 46or so grains I had a drop in velocity at the next level 46.5grs the velocity was back where it should have been.
Make sure you powder at the correct weight.
and bullet tension is the same. If you anneiled the necks that would make a diffrence if you have shot the brass 3or 4 times the necks will work harden changing tension on the bullet.
I have found ir necessary to adjust loads due to temperature changes that were extreme changes.
A pretty good way to tell is to keep a group of loaded ammo warm then shoot a 3 or 5 round group see if that does affect the load.
Dave

Sorry it seems that no matter what or where I am posting I always leave out one piece of vital information. I am loading for the 30-06 and all of my loads have been using the same Federal cases. During my first trip to the range all of the brass had been once fired and on the trip yesterday it was the same brass only twice fired, both time they had been FL resized using a Lee pacesetter FL resizing die. I am thinking about annealing the cases after I fire them one more time.

Emorr:

The answer is YES, temperature can have that much of an effect.

In the .270 Win, with H4831, the difference between 70 and 95 degrees is usually around 100 FPS.

For this reason, anytime I chronograph a new string, I like to overlap with the previous string, so I have a point of comparison.

I have found H4831 to be pretty much insesitive
to extreme temp changes in any of the calibers I load for. 25/06 .243 .270 to name three. A fact that warm air is thinner or less dense than cool air. As a result, a bullet encounters less resistance and expends less energy as it travels from the firing line to the target on a warm day than it does on a cooler day.
do a test throw some in the freezer keep the as cold as possible and go to the range do the same place some on the floor and let the car heater warm them up see what affect they have on velocity and accuracy. I am sure you will see something but it probably wont ammount to much. the one thing I do know is that altitude will play a game on you. air is less dense at 5000 feet compared to sea level the diffrence can be as much as 150f/s increase in velocity.
On a relatively cool day (50 degrees), the outside air is able to absorb more heat from the barrel at a faster rate than it does when the air temperature is 80 or 90 degrees. This helps to keep the barrel cooler with fewer harmful side effects like “baking” the fouling in the barrel which in turn can result in a significant loss of accuracy and increase in velocity.
the amount of humidity in the air has virtually no effect on bullet accuracy. That’s because a water molecule weighs less than a dry air molecule. Moist air is actually less dense than dry air.