Perplexed by slow loads

mdmp5

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  • May 7, 2009
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    Today I chronied a bunch of loads in both .223 and .308 and they were all at least 100 fps slower than expected. The one that really had me scratching my head was 155 Palmas over 45 gr of RL15; yielded about 2650 fps. This is crazy, as I expected at least 2800, from what my shooting solution was revealing last session. Anyway, does this velocity sound super slow to you guys? This was out of an SPRA1a w/ a 20" bbl BTW.
     

    BobinNC

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    Re: Perplexed by slow loads

    palmik,

    Max load according to Alliant is 49 grains RL15, for right @ 2900 FPS. So 2650 from 45 grains is not surprising, but still a bit low, IMHO. From a 20" barreled bolt gun, I would expect no more than around 2850 FPS from a max load. Don't know about a gas pusher.....

    Shoot it's hard to get 2800 FPS from 45 grains of Varget, much less RL-15. I need 46.5 grains of Varget to hit 2800 FPS from a 20" barreled LTR.

    YMMV,

    Bob
     

    MitchAlsup

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    Re: Perplexed by slow loads

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Anyway, does this velocity sound super slow to you guys? This was out of an SPRA1a w/ a 20" bbl BTW. </div></div>

    Slow? No not really. It may be slow, but you are far from any useful pressure sign.

    Also note its going to be difficult to ge tthe 2900+ fps we like from 20" barrels unless your load is right near-but-under the typical pressure signs.
     

    mdmp5

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    Re: Perplexed by slow loads

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Victor N TN</div><div class="ubbcode-body">What kind of chronograph were you using?</div></div>

    It wasn't mine; it was a CED 2 to the best of my knowledge. It was the property of the range. I have to admit that I don't think I really trust it anyway, since it gave me an extreme spread of 100 on a batch of loads! But in any case, it was a ballpark estimate of my speeds, so it helped a little bit; but it also hurt too.
     

    mdmp5

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    Re: Perplexed by slow loads

    Oh, the chrony was covered up by a big mailbox looking cover. You think that affected its accuracy?
     

    XMC

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    Re: Perplexed by slow loads

    I have several loading manuals from 25 years ago up to a current Nosler manual and it's scary how much heavier the loads are that are listed in the older mauals. Not all powders from back then are avaialble in the newer books but the ones that are seem to be lower charges now, better data or liability issues? The listed velocities per powder charge seem to vary considerably too.
     

    Powder_Burns

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    Re: Perplexed by slow loads

    I know the Chrony's units fold out and if it is not completely folded open the distance to the sensors would be off, but that results in higher FPS readings. If your lighting was changing a lot it could play a role...your seating depths, primers, and neck tension could as well.