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Thread: Small rifle vs small rifle magnum primers

  1. #1
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    Small rifle vs small rifle magnum primers

    Apologies in advance: my eyes glazed over reading search returns.

    Anyway, loading plinking ammo. Using up an assortment of OLD primers. Happy load with 55gr fmj, 24.2-24.7gr Shooters World AR Plus (I understand 26.2gr to be suggested max) cci 400 primers, lc brass. KIM, plinking ammo so would rather not waste components on further load workup (after these cci's loaded, will be down to 100 of these, 60 of those, etc.).
    Question is: How worrisome are effects of going from "standard" small rifle primers to magnum primers (Win SR Magnum in this case? Was hoping to just load everything on out with 24.2 or so grains and blast away.

    Thoughts?

    Thanks

  2. #2
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    The military generally uses the equivalent of commercial magnum primers for 1) ensuring ignition in the cold and to compensate for aging/oxidizing powder and 2) thicker primer cup material to prevent primer punctures.

    CCI 400 primers have thinner cups (.020-inch thick) than the 450 magnum (.025-inch) primers. Great for something mild like M1 carbine, on the border for higher-pressure .223 / 5.56mm in the summer, mid-day in the desert.

  3. #3
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    It sounds like you're worried about the magnum primers pushing your plinking loads over into some kind of over-pressure...

    Since you're so far below the max powder charge, it's probably a non-issue, but I'd be curious to see how the cartridges loaded with magnum primers chrono vs. those with standard primers.

    Also, AFAIK part of the reason for thicker cups in "military" primers (CCI #41s) is to prevent slam-fires in self-loading rifles. It's an open question whether that's a real hazard, but I'll only use CCI 41s...

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    Although not a "scientific" test by any means I found this two part 223 primer shootout informative. It appears that the standard vs magnum small rifle primer the usual cautions are a bit overstated.

    https://www.youtube.com/watch?v=N7KVBWChnyY&t=1044s

    https://www.youtube.com/watch?v=GaYKzLHWYvU
    Last edited by BobinNC; 09-23-20 at 14:44.

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    Yeah, more worried about pressures. Having re-checked, I'm closer to 223 starting load than max and 556 load appears .7gr higher than 223. Will check out suggested vids soon. Might even just load em at 223 start load and blast away. Thanks, again for the input.

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    Quote Originally Posted by sinister View Post
    CCI 400 primers have thinner cups (.020-inch thick) than the 450 magnum (.025-inch) primers.
    Quote Originally Posted by Bimmer View Post
    Also, AFAIK part of the reason for thicker cups in "military" primers (CCI #41s) is to prevent slam-fires in self-loading rifles.
    What is the cup thickness of the CCI 41 primers?

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    I use CCI450s for everything.

    Everything.

    9mm. 223. 6.5 Creedmoor.

    Everything lol

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    Quote Originally Posted by Disciple View Post
    What is the cup thickness of the CCI 41 primers?
    0.025" same as the CCI 450

  9. #9
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    Primers can have a noticeable impact on a load. Like Bimmer said, you're fine with whatever since you're not flirting with max pressures.

    I've seen a velocity increase of 40 fps in a .223 load with only the primer as the variable. I think it was Fed AR Match vs Wolf SRM, with the Federal primer yielding the higher velocity.

    Another thing to note, "Magnum" doesn't necessarily mean a hotter primer. Wolf SRMs for example have a thicker cup, but are a really mild primer.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

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    Dadgummit Bimmer. As to your wondering about side to side comparison of std and mag: have realized that acceptable load workup was actually with WSR primers. Magnums were Gold Medal Match. So, I have those along with Fed Small Rifle, Fed Small Rifle Match, all 15yrs old or so. And I have 2 yr old Fed AR Match. May have to run down a buddy with his chrono. So much for just shooting rocks?

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