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Thread: 556 flash hole specs?

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    556 flash hole specs?

    What is the diameter spec for 556 flash hole. Can't find hard data. Thinking 078-080,but have seen the 082 which I think is large rifle. I know different brands will be diff dia, but I want to uniform some LC22 range pickup.....

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    I'd suggest you purchase a pin gauge set and determine what you already have, then decide what median diameter you want to settle on. I'd imagine that there would be some potentially wild variations out there. SAAMI shows specs for .223 cases, but since NATO specs aren't necessarily the same as SAAMI you may have some leg work to do. I looked briefly and didn't even see a SAAMI spec for flash holes.
    “Detached Reflection Cannot Be Demanded in the Presence of an Uplifted Knife” ~ Brown v. United States (1921)

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    Quote Originally Posted by anachronism View Post
    I'd imagine that there would be some potentially wild variations out there.
    Yeah. Some of that damned import ammo has flash holes so small, my decap pin won't fit. I was going to open them up, but it became too big of an ass ache.

    Honestly if uniforming flash holes became THAT critical, I'd just buy some LaPua brass. The proverbial juice isn't worth the squeeze. Getting the same year headstamp should be good enough.
    "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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    I pin gauged some once fired LC 90 and 12 and they ranged from between .077 and .081.

    I'd use .079 as my nominal goal based on this data set as measured by me.

    But I don't fuss about primer pockets anymore, I don't even clean them as I've seen zero evidence it has any impact on accuracy. I do have evidence that case volume impacts repeatable accuracy potential for a given loading and I do spend the time to sort by head stamps, when loading for accuracy.

    Still looking for some new Lapua cases to measure. So I may be back with more data.

    ETA: All my Lapua is sitting loaded in boxes, the single once fired case I was able to find measured .080 so maybe I'd shoot for that instead.
    Last edited by HKGuns; 12-05-23 at 16:23.

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    Unless the flash holes were really wild and all over the place, I'd bet that the primer quality would be more significantly impacting consistency.
    "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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    Quote Originally Posted by triggerjerk View Post
    What is the diameter spec for 556 flash hole. Can't find hard data.
    GI mil-standard is .080 ~ +.004


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    Thanks, guys, esp sinister, and yes, I too doubt FH dia makes any diff for AR accuracy, but it's the easiest part of working brass (for a bored old man). I was drilling 080 and ignoring the loose holes. And now I may start using my old Sinclair fh deburring tool since 082 seems to be within reason. And the only reason I uniform pocket depth is in hopes of reducing shallow pockets interacting with civvy primers and floating firing pins... I waste a lot of time in reloading so I can blame poor performance strictly on myself for not having my eyes closed or on not pulling the trigger hard enough....

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    Sinister for the win! That makes sense based on the readings I was taking and that LaPua was right on the money.

    Wasn't trying to tell you not to do it.....Your brass, your process. Just letting you know I didn't for a single data point that is probably meaningless.

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    Quote Originally Posted by HKGuns View Post
    Wasn't trying to tell you not to do it.....
    I was!
    "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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    No sweat HK. I try to check a lot of boxes that, in the end, have absolutely no effect on the results, especially given my equipment and skills. It is mostly about making honest effort through each phase of the journey for me at this point.....

    Was typing as markm posted, so, how bout this:

    I think you're both right!
    Last edited by triggerjerk; 12-05-23 at 20:44.

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