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  1. #1
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    Default More .357 Magnum testing

    This time the Sierra 140 gr. JHP is the bullet set with a C.O.A.L. of 1.585". Added A#5 powder to the test loads because I have it on hand and it is included in the Sierra Manual Ed. 5, which is the source for this round of testing.
    Practically everything else is the same. Including the feeling of confusion I get when I look at the results! I still find a few instances where heavier powder loads give lower velocities and some cases where the increase in velocity is very small for the increase in powder weight.

    I got to thinking also if there's an established way to evaluate the "efficiency" of a powder at a given charge and bullet. For example 19.4grs of 296 gives 1277 fps (average) and the same weight of H110 yields 1228 fps. If I divide the velocity by charge weight I get 1277/19.4 = 65.8 fps/gr and 1228/19.4 = 63.3 fps/gr. Therefore I can judge that 296 is more efficient than H110 which seems to hold since it gives higher average velocities for all but one charge weight. If I toss in A3% at 10.6 gr. with a velocity of 1181 I get 1181/10.6 = 111.4 fps/gr. Outclassing both of them for this bullet. Unfortunately it hits its maximum at 10.8 grs.

    Found a jug of Blue Dot at an LGS. With luck the weather will stay good enough so I can get one more round of tests in and go right to the carbine.
    Attached Files Attached Files

  2. #2
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    Default Re: More .357 Magnum testing

    Just a thought based in part on my black powder experience. Is is possible the higher velocity with the lower powder charges is because the larger charges are not fully combusting before the bullet leaves the barrel and a part of the explosion is wasted on muzzle blast/flash. If this is the case the results from the carbine with a longer barrel should be interesting.
    Illegitimus non carborundum est

  3. #3
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    Default Re: More .357 Magnum testing

    ^^^^! That's pretty much what I've been thinking! Consequently the loads I'm considering the most desirable for the carbine are not the heaviest, but those with a "better" SD and close to the top velocity.

  4. #4
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    Default Re: More .357 Magnum testing

    Quote Originally Posted by Brick View Post
    I got to thinking also if there's an established way to evaluate the "efficiency" of a powder at a given charge and bullet. For example 19.4grs of 296 gives 1277 fps (average) and the same weight of H110 yields 1228 fps. If I divide the velocity by charge weight I get 1277/19.4 = 65.8 fps/gr and 1228/19.4 = 63.3 fps/gr. Therefore I can judge that 296 is more efficient than H110 which seems to hold since it gives higher average velocities for all but one charge weight. If I toss in A3% at 10.6 gr. with a velocity of 1181 I get 1181/10.6 = 111.4 fps/gr. Outclassing both of them for this bullet. Unfortunately it hits its maximum at 10.8 grs.
    All smokeless powders have the same amount of "energy" per grain. It is just that some release the energy faster (burn faster).

    What makes a bullet move is the pressure x the time it is in the barrel. A fast powder like bullseye will ignite almost instantly so it will get to full pressure quickly. Unfortunately the pressure spike doesn't last that long. So you need a slower powder that keeps pushing the bullet out steadily. But going too slow gives you low pressure / erratic pressure and wasted powder. Every cartridge has a burning rate sweet spot. Looking at the reloading tables there is always one or two powders that give the highest velocity. Those are the ones that will fill the case to 100% and have the optimal burn rate.

    H110 / W296 are EXACTLY the same powder. They were always made by the same company in bulk then rebranded. The velocity difference you see is just lot to lot variations. One of your lots is faster than the other. That is why they always say if you buy a new lot of a powder you are supposed to back off a little ande work your max up again.

    Also H110 / W296 is on the slow side for a 357 (especially for a 140 grain bullet). Try HS-6.

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