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Thread: Psi ?

  1. #1
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    Default Psi ?

    Just starting out loading for the S & W .500 and I find quite a bit of data on different weight bullets and powders. I was wondering how the PSI is determined and what the difference is when using large rifle primers and large rifle magnum primers? The charts of course don't list all bullet weights so if they skip a 300 grain bullet and go from 275 grain to 325 grain if it safe to load a 300 grain a little lighter than the 325 grain using the same powder considering the data used is for the minimum loads?

  2. #2
    Moderator Paul H's Avatar
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    PSI is measured in a laboratory with a special test gun.

    I can't say what the affect is on pressure when going from a large rifle std primer to a magnum primer as it will depend on the powder. Here is a reandom google image of the pressure in a firearm when it's fired:



    When pressure is discussed it is the peak of the pressure curve. The thing to remember is that changing components doesn't just change the peak of the curve, it can change the shape of the curve as well. Hence going to a hotter magnum primer might actually reduce the peak of the pressure curve as it affects how the powder burns and hence the overall shape of the curve.

    As far as interpolating data for a bullet weight that falls between weights with published data I've personally found if you are comparing the same style of bullet with similar bearing lengths you're generally good to go splitting the difference in the powder charge weights and working up your load.

    The one big caveat is with H-110/W-296. Always heed the advice not to load it less than the starting loads. It's one powder that can be very dangerous to load lightly.
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  3. #3
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    Default

    Thanks for that info, interesting. I don't have any H 110, I probably would have but powder is messed up like .22 lr is. Just hard to find . The powder I was working with on the 300 gr FTX is Longshot. I'll be using H 4227 also but so far I've not actually found any loading data for that bullet with those powders.

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