Topic: Powder Temperature Sensitivity

[emathey]

So BoiseShooters, I understand that some powders are sensitive to temperature and pressure can vary depending on the weather.  I currently use H335 to reload .223  for my AR-15 and I've ran some test loads through my gun this month, can I assume that anything that was tested during one of the hottest months of the year is going to be good to go the rest of the year?  Does this change velocity at all, or is it just the pressure that varies?

[ballardw]

Pressure change will affect velocity, the question is how much. Consider some of the overbore magnums where noticeable changes in pressure only net a few extra fps.

If the load is on the mild side, i.e. near minimum, in hot weather you may get low enough pressures in (extreme) cold that powder burn gets a tad erratic like with under minimums. Maybe.

Chronograph in both conditions and see.

I think the more serious concerns come with cases with much larger case capacity as more powder = more chance for high pressure.

[2big2fail]

Put 10 rounds in the freezer, then put them in a cooler with ice.  Leave 10 rounds on the dash in the sun as you head out to the range with your chrono.  Shoot the cold ones first (naturally). Then take notes.  You will see a noticeable difference in velocity between temperature groups.  I've tried this myself and depending on case size (rifle vs pistol) I've seen up to 123fps variables.   "VihtaVuori", it has been rumored, has the least fluctuation at different temperatures  There may be others, I don't have a chart, but that's what I've got on the subject so far.
     - Oh yea, also bullet weight has an influence in the formula.  ex: a 22-250 with a 55 grn bullet will fluctuate a great deal more than a 45-70.  As the bullet gets lighter, the coefficient scale of variation is exponential.  I'm sure that somewhere on this planet there's a formula, but I haven't found it yet.

[Nealio]

My .223 loads go from a .5" group to a 6" group between mid summer and mid winter....
I'm using Win748 though, which is rumored to be one of the most temperature sensitive powders.  I haven't chrono'd them in the winter (I learned to just not shoot them).

I have some of that new IMR 8208 XBR benchrest stuff J Mack mentioned months back, but I haven't loaded any of it yet.

[Bill, Idaho]

In several sniper schools I've been to, they have taught temperature will make a noticable difference.  The common formula was a minute for every 20 degrees.  Our guys have found that to be pretty close.   Maybe not a whole minute, but thereabouts.   

Another thing to consider (not exactly within the realms of this particular subject) is the temperature of the ammo and weapon as well. Even the time the round is in the gun matters, when you get into the fine tuning of all the variables.

I don't know if the temperature of the powder itself is as important as the sum of the temperature variables I mentioned.

[birddog1989]

I use Varget in my 308 and shoot the same poa/poi in January that I do in August.

[egress81]

I made sure to try and find powders that I can use in all weather, Tac and Varget have worked great so far and I have good results with Retumbo so far, even with major altitude changes (from 4500' to sea level)

I have never chrono'd any of these loads, but from I have shot for groups in temperatures ranging from 10* to 90* weather and in my experience I haven't noticed a significant decline or increase in accuracy/poi.

[adrewiske]

LRP Episode 12 Management Deer at a Half Mile

Minutes 8-11 have a good demo and explanation on this.

[tgibson]

I shoot a little long range and have done so in the heat of summer and the dead of winter.  Shooting 118LR, I've shot 1/2 MOA groups at 200 yards at 90 degrees and 15 degrees.  Take it for what its worth.
Adios,
TG

[MtGoat]

Back in the day when shooting high power, we use to store our ammo in coolers and limit chamber dwell time as much as possible.  May be an old wives tale but never tried bucking the system

Pat

[Nomad]

Back in the day when shooting high power, we use to store our ammo in coolers and limit chamber dwell time as much as possible.  May be an old wives tale but never tried bucking the system

Pat
 Have to go with MtGoat as to store your ammo in a cooler no ice as well as out of the sun and don't let it set in the chamber too long.
 Opinions will vary as stated earlier different things to think about....

[44magnut]

I use a lot of VV powders. POI has very little change do to the temp change, high on a hill or down along the Snake River valley. I know it is a little $$$, but well worth the $$$ money to me when I know that everything is the same no matter where I’m at. My 223 and 223IA I use N-130 and N-133.