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chamber pressure and air temp?

260
ok guys. my uncle and i have been having this argument for years and now i want to know what you all think. i tell him that with some powders near max. that chamber pressure can rise when it is warmer . i have some loads that i can shoot below 72 deg. with no problem. when it is hotter say 85 deg. bolt lift is stiff.what do you think?
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5 comments

Date Votes
  • mark christian
    Tests conducted at the Frankford Arsenal, Burnside Laboratory, and a number of private European firms like Pachmann & Wurzle dating back as far as 1928 have shown a direct link to changes in pressure as well as muzzel velocity due to ambiant air temperature. The US Ordnance Dept. actually developed a curve which used a benchmark 70 degrees F. for our 30-06 service cartridge and this chart shows an increase in velocity of 1.75 fps for each degree of temperature increase up to 140 degrees F. I cannot find the exact data curve on pressure changes, but it was mentioned by the Ordnance Department's report and temperature does have a direct effect on pressures to some extent.

    Mark T. Christian
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  • JustC
    the increase in pressure is related to the burn rate of the powder as well as it's chemical composition and it's coatings. Powders can be very temp sensitive (RL22 is one IMO) and then they can be temp "insensitive" (take that with caution,..they are all sensitive to some degree) H1000 is less temp sensitive,..just as an example.

    why chase the game when the bullet can get em from here?....
    Got Balistics?
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  • temblor
    Ditto what Mark & Justc said....................It absolutely affects pressure and velocity. I live where it's warm so I tend to work up loads when it's warmer and then they shoot fine in the colder months -- but not vice versa. If you work up a near max. load when it's cool your increasing your chances of pressure problems when it warms up -- seen it many times.............[8D]
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  • 260
    thanks guys, i've been loading for 30 yrs. what temblor has to say is right on.now just maybe ,i can close this chapter.
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  • boltthrower
    So what does your uncle buy?
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