Does a bullet travel faster in hot weather?

Discussion in 'Reloading' started by Bigcat_hunter, Jul 22, 2007.

  1. Bigcat_hunter

    Bigcat_hunter Well-Known Member

    Dec 8, 2006
    I am working on a load and just used a chrono for the first time. It was about 91 degrees outside. The load in the sierra book said a 300 smk should be traveling 2700 fps with a 26" barrel out of a 338 RUM w/92 g. of H1000. My bullets are traveling over 2800 fps. Is this do to the hot weather?
  2. britz

    britz Well-Known Member

    Mar 11, 2007
    As far as I know, bullets do travel faster in warmer weather generally. This is mostley due to the air being thinner and having less friction in warm climates thought. I don't think you can safely assume that the temp has the only influence on muzzle velocity though. I am sure temperature will impact a little. Some powders are more vulnerable to temperature differences than others too. I would guess that it has more to do with your chamber dimentions, rate of twist, seating depth, and throught of the rifle that you are shooting verses the those charectoristics of the test barrel.
    but I could be wrong too lol! good luck

  3. James Jones

    James Jones Well-Known Member

    Jul 1, 2002
    100 fps is a pretty big jump in velocity , I know that the warmer air is less dense but I seriously doubt that even a 60-70 deg differance will make a 100 fps differance in velocity. I would wager to say that your big jump in speed is due to the powder being temp sensitive more that the air density .
    BUT , not sure if you had shot this same load in cooler weather but alot of times some barrels will shoot a good bit faster with a given load than what the books say. I have a 25" 1-11 twist Obermeyer on a custom 300 win mag thats shoots almost 100 fps faster than any of the books loads with a 26" barrel. , some barrles are just fast.

    I know a guy that still hase a Remington 700 , fully blue printed and had a 26" Pac-Nor barrel installed , chambered for 22-250. H built the gun just to shoot 50 gr bullets as fast as possible for ground squirrels. he worked up a very hot load in January (30 deg) with H-380 that was flatteniong and loosening primer pockets with one firing. The gun sat dormant till his trip to California (July 90+ deg) where he took it out to check zero and fired it one time and it galled the bolt closed. He has since made the gun into a decoration for his reloading room
  4. edge

    edge Well-Known Member

    Nov 4, 2005
    IMO, muzzle velocity increase is due to the temperature sensitivity of the powder.

    Long range retained velocity is due generally to more moisture in the air which is lighter than air with low humidity. Airplanes may easily require 50% more runway to take-off in the Summer than they do in the Winter to compensate for air density.