Powder temperature sensitivity

Discussion in 'Reloading' started by Coach Hunt, Nov 29, 2009.

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  1. Coach Hunt

    Coach Hunt Well-Known Member

    Jun 22, 2009
    Fellow shooters,

    I've mostly used Hodgdon, because that is available locally. IMR powders I've used were much "milder" in freezing temperatures. I want to improve velocity in one cartridge, and the manuals show Ramshot's Magnum powder and Accurate's Magpro powder to give 150 to 200 fps more velocity than what I can currently get with either H4831 or H4350... The Hodgdon based velocities are measured on chrono. RL17 proved to shoot a full 200 fps faster in this cartridge than either Hodgdon powder used. I've read several threads about the RL17's temperature characteristics, but nothing on the Magnum or Magpro powders. What I MUST know is: What is the relative temperature sensitivity of each of these powders??? I ask because I must work up the loads near 75 degrees, yet hunt at freezing or below. Which will be more stable throughout the temperature range??? Who can help???


  2. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    Nobody knows their temperature sensitivity without testing it in their gun. This is what you will have to do.

    Or, you can keep ammo in your pocket, and load single shot -just prior to taking a shot in cold temps. With that, you have only the POI change from a colder barrel. This could still be significant if not cut-rifled.
  3. johnnyk

    johnnyk Well-Known Member

    Dec 24, 2001
    Hey Coach,
    I use alot of different powders year round, with the exception of AA and Ramshot, and I notice a little difference in velocity, but not alot. I usually adjust my Ballistic Card according to the conditions I'll be hunting in.
    For instances; if I'm hunting groundhogs with my .243 Win and a Hornady 75gn HP/IMR 4895 in 90-80 deg temps., first thing I do after I've found an accurate load is chrono that load at that temperature, and at the same time check my zero. For "whistlepigs" I like the zero to be approx. 3-3.5" high @ 100yds and dead on at 300yds. I make my card up and use that as long as the ammunition last, the conditions persist or the groundhogs wave a white flag :).
    After I print out that data, I cut only the necessary info out, write the load data on the back (i.e. cartridge/bullet/powder/primer/case/OAL/velocity/date) and the atmospheric data (i.e. wind/temp/humidity/barometric pressure), then I laminate it so it can easily be taken and replaced from behind the nylon cartridge carrier on my rifle stock.
    Later, if I switch to the 95gn Ballistic Tip/Viht N560 in 60-50deg temps., I make a card for that only after I chrono the most accurate load.
    This is not the preferred method for everyone, but it works great for me, it's quick and it's accurate. JohnnyK.
  4. lowrider

    lowrider New Member

    Apr 13, 2011
    I have been shooting Magnum powder through my 338 Lapua for over a year now. I love this powder as I have shot many groups placing 3 shots being covered easily by a dime. Loads also prove to be very stable & consistent with an SD of 3 on a 4 shot string. I also have been looking for some info on temperature stability on this particular powder. Please see the link I have attached & you will see that according to Barnes testing this powder proved to be a very thermally stabile powder.

    Hope this helps???

    July 2010 Barnes Bullet-N | Barnes Bullets
  5. Lefty7mmstw

    Lefty7mmstw Well-Known Member

    May 13, 2012
    but if you are at -10 degrees with a wind your pocket will still be at freezing. You should shoot at the temp you will be hunting at to be sure, but I realize this isn't always possible. If I couldn't hunt with a load I'd vetted in both hot and cold temps. I'd go with THE ONE THAT SHOWED THE LOWEST ACCURACY FALLOFF AS I DROP THE CHARGE WEIGHT, and I'd hope for a slight gain in accuracy. If your load is see-sawing between great and crappy accuracy as it pulls in and out of node when you pull the powder charge up, the load is crap and I won't touch it period.
    Don't use a mild primer either, as under igniting will cause a squib on occasion-- with a bullet in bore chance, or poor accuracy at least with long lock-time. Over- igniting with a hot primer just pushes your pressure up a bit.
  6. BradS

    BradS New Member

    Jul 27, 2015
    I have results from the weekend testing that I did to determine temperature effects on cartridges. I have been experimenting with the same round for about 2 years and have worked up a load and controlled as many variables as possible. I have seen that the velocity is about 1% higher with cold Retumbo powder VS a warm Retumbo powder load. I have also seen that low primer weight hurts the velocity. I am surprised by the temperature correlation, this does not follow the other results that people have posted previously.

    Summary Results (July 25 2015):

    1. -20C VS 25C cartridge (as described below) is ~1% faster for the cold cartridge.

    2. Low primer weight is nearing 1% slower than nominal or high primer weight. I have done this experiment 4 times now, there is a definite correction on CCI 250 and weight.

    Here is the experiment:

    Cartridge: 7mm Rem Mag
    Brass: Norma (I have weighed it all to within +-1.5grains.)
    Bullet: 150.2grain Barnes T-TSX

    Primer: CCI 250, (1 lot) Weighed to 5.18grains (0.02grain resolution on the scale).
    Powder: Retumbo, 75.0 grains, (all one lot)
    Brass: fired 6 times, at max brass length, never trimmed, but still in spec.
    Neck Resized: 0.311"
    Headspace: 0.008"
    Finished Round: 3.10" setting - Redding dies (Measured to be 3.15-3.19")
    Concentricity: +- 0.002" (not corrected, just measured)
    Load Environment: 72F, 50% humidity (estimate).
    Equipment: RCBS digital powder measure, Redding competition dies.
    Gun: Sauer 202

    Final Ammunition:
    Label (1a) As above but 20x rounds with primers at 5.22grains.
    Label (1b) As above but 20x rounds with primers at 5.14grains.
    Label (1c) As above, nominal 40x rounds with primers at 5.18grains.

    The Experiment:
    1. cold soaked 10 rounds of the (1c) above at -20C for 8 hours, put them in a cooler with thermal mass at -20C.

    2. Using a Magnetospeed-V3 Chronograph, I shot 1 shot out of a clean gun, then waited 90s I shot the following sequence:
    - 1 shot (1c, 5.18gn) @ -20C), wait 90s
    - 1 shot (1c, 5.18gn) @ +25C), wait 90s
    - 1 shot (1b, 5.14gn) @ +25C), wait 90s
    - 1 shot (1a, 5.22gn) @ +25C), wait 90s
    - Repeat the above 4 shot sequence 7 more times, for a total of 32 shots.

    A) The cold ammunition was shot with 10s of being removed from the cooler.

    B) The gun got hot, but not too hot to touch, my shotgun gets a lot hotter when I do 25 shots at trap shooting).

    C) I have changed my Chronograph to the Magnetospeed-V3 last year to eliminate the error caused by the equipment. (the Magnetospeed clamps onto the barrel). I had been using an RCBS Ammo-master, however the error caused by the placement of the sensors each time was +- 30fps. It made the measurements impossible to correlate:

    -First shot 1-shot average 3048fps.
    -(1c @25C) 8-shot average 3053fps, Spread 28fps.
    -(1c @-20C) 8-shot average 3080fps, Spread 60fps.
    -(1b @25C) 8-shot average 3027fps, Spread 40fps.
    -(1a @25C) 8-shot average 3049fps, Spread 24fps.

    Average for all 33-shots, 3061fps +- 50fps (3011fps to 3111fps)

    I went back though my notebook and found an identical load that I shot on October 30 2014 with the same lots of powder and primer. The 11-shot average was 3070fps at -2C. I am going to keep the ammunition until the outside temperature drops to 0C and repeat with -20C, 0c and +25C ammunition from load labeled (1c).

    Has anyone ever seen these kinds of results? Could it be something to do with the bullet friction on the barrel etc...? (these are full copper bullets)

    FEENIX Well-Known Member LRH Team Member

    Dec 20, 2008
    Checkout #2 (esp. the last 2 paragraphs) of http://www.longrangehunting.com/forums/f28/powder-temperature-sensitivity-31096/
  8. jonthomps

    jonthomps Well-Known Member

    Dec 2, 2005
    This ^^^ is great info. I've had great luck with H1000 be temp stable. I'd like to hear what others have to say about Retumbo temp stability. I've heard it's supposed to be pretty stable. Anyone tested N570 for temp stability?