powder temperature sensitivity

[s64woody]

Worked up loads for a .308 using surplus WC844. Silly stuff gets better velocity with heavy bullets than most anything that I have worked with, but I am starting to wonder if a somewhat more moderate loading in better due to what I remember about ball powder temperature sensitivity.
Load development was at about 70 degrees, and I occasionally shoot in places where 100 to 110 degrees is common. Anyone out there have the real scoop on this characteristic of ball powder?

 

[Steve Smith]

Ball powders are notorious for being more temperature sensitive as a whole. You should be careful and download your ammo during very hot weather or keep it cold in a cooler with ice. Otherwise, you could switch powders.

 

[s64woody]

Thank you Steve
That is pretty much the plan. I was hopeful that there was some rule of thumb or such that would give me a starting point on where to shut off the powder measure in moderate temps.
The WC844 is easily pushing 174 gr. boattails out of my PSS at mid 2700s(!!!), but I feel that the higher temps the ammo may go to will require some downloading. Just how much is the key .
Example: Someone out there is savvy enough to know how much point of impact shifts with each degree of temp increase. You can calculate the velocity change that would require, and I know what the curve on the powder is, so I could figure out what to load at the moderate temps....
thanks all
woody

 

[Steve Smith]

You have to spend a lot of time with each caliber and bullet to work out somthing like that. Altitude will play a part too. I don't know of any reliable rules of thumb on this. I don't know of anyone in the long range competitive sports that uses ball powder.

 

[C.R.Sam]

Nuther thought.
Steves info invaluable.

Would like to add...
Quite often best accuracy is obtained at less than max load.

Sam

 

[Steve Smith]

Sam's comment is a good one. Also I thought I should add that while none of us use ball, we all want to because of the metering. Some use ball in one season only, or have multiple loads...which could cause a mistake and a disaster.

 

[wingman]

Quite often best accuracy is obtained at less than max load.

Found this to be true in both pistols and rifles. Why load to max. for target
shooting.

 

[Steve Smith]

Close to max can bring some benefits IF accuracy is acceptable. Loading to max for long distance reduces the flight time and therefore the amount of wind deflection. Again, ONLY if accuracy is acceptable.

 

[s64woody]

All of the comments are valid.
I know that the M-118 round was loaded to about 2575 or so, and I have absolutely no desire to max anything out. I do have some problems with the PSS stabilizing heavy bullets...of course everything is measured against the 168 gr. Match King.
I was looking for higher velocity only in the attempt to gain more downrange stability. The 173gr. M72 bullet is pretty good for an arsenal projectile, but it will never ever be a MK.
I had never heard that most or all of the match shooters use an extruded powder.

 

[Steve Smith]

Try a 175 MK.

 

[Grump]

In .308 using Sierra 168s, I got almost exactly 1 fps change in velocity per degree farenheit outside when fired, from mid-40s to about 100 degrees. You *may* want to plan accordingly--if your "max" book load shows X fps at 78 degrees, back off if you get that speed from the same length barrel at colder temps.

 

[wanderinwalker]

Found this to be true in both pistols and rifles. Why load to max. for target

Exactly. My .223 target loads consist of 24gr of W748 (Ball Powder) and a 69gr Sierra MatchKing for about 2575 fps. I know that this load works well for 200 and 300 yard shooting. After we burn off the 3 pounds my dad bought I may go to Varget, as I have had extremely good luck with other Hodgdon powders in my .260 Rem and an 03A3.

 

[s64woody]

Grump Interesting data. I like the idea of using the velocity available from the WC844, but allowing enough cusion to be safe at higher temperatures. I guess my range data book will have to include a temp gauge from now on so that I can collect this data. Why I never included this information in the past puzzles me......duh. I will try to verify the 1 fps per degree of temp change.

 

[Grump]

Interestingly enough, I think it was the 1971 Sierra reloading manual that said reloaders could not duplicate factory velocities in the .308 until the Winchester Ball(tm) powders came out.

 

[Clark]

I cannot prove it, but my guess is that a chamber that just fired 5 shots is allot hotter in a snow storm than a chmaber that has not fired on the hottest day of the year.

 

[s64woody]

Clark... I suspect it has to do with the temperature of the powder, not the chamber...grin. Actually, the testing is done, as I remember, with what they call "conditioned" ammo: chill or heat it to the appropriate test temp and maintain it there til it is shot. Another good reason to have a cooler at the range!
Grump, I gots to go to my library and see what I find. Tis amazing the info available to us, if we but knew the question to ask.

 

[Adventurer_96]

http://www.gunsandammomag.com/ammunition/match_0620/

Here's a link with some 168gr Sierra loads.

I've been interested in Ramshot's TAC powder lately because it's been described to me as being much more temperature stable. Here's a link to a thread at snipershide http://www.snipershide.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=13;t=000649 on a temperature test between TAC and Varget.