Flas Hole Question
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  1. #1
    Marlin Marksman
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    Flas Hole Question

    I am hoping that someone with more experience than I have will be able to give me some insight. The Staying at home thing has let me catch up on projects I have been putting off, one of them is cleaning up about 600rnds of 45 acp brass that I have been storing in a couple of coffee cans for several years. Some of the brass was from what I fired and some of it was scrounged range brass. After I cleaned it up I was inspecting some of it and was surprised at the difference in flash holes. The Federal brass had large holes with some being elongated, the Winchester and the Starline's flash holes were about the same and some marked S&B had smaller holes. I do not remember this with any of my rifle brass but maybe I didn't look close enough.

    My question is will this make any practical difference in my reloading of this brass. I will probably separate it when loading but would this affect pressure with my high end loads. Thanks

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    Gun Wizard
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    good question, hopefully someone with ballistics expertise will chime in. I guess I'm a practical reloader. if the flash hole is open and the case had fired a bullet previously I reload it.

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    For match ammo segregate them by size. Size matters, especially for rifle ammo. Bigger hole, faster ignition, a slight pressure rise, and velocity increase. For blanks, you need to open up the hole so the primer won't walk back hanging up a revolver.

    AC

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    Nominal spec for flash holes is .0625" for small primers and .0810" for large. It will vary a little from different manufacturers. When I was young, an article I read recommended getting an .083" drill bit to clean up the flash holes so they would all be uniform. The decapping stems are alleged to be .083", but I've never measured one.
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    Quote Originally Posted by gunscrewguy View Post
    For match ammo segregate them by size. Size matters, especially for rifle ammo. Bigger hole, faster ignition, a slight pressure rise, and velocity increase. For blanks, you need to open up the hole so the primer won't walk back hanging up a revolver.

    AC
    Ages ago it was explained to me that smaller holes develop more "pressure" in the pocket which leads to a more powerful flame jet into the powder leading to a faster burn.
    Another explanation I got for hole size is that it depends on the powder used to load since you didn't want it going into the primer.
    Does make you wonder what really happens...
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    I use a uniforming tool to remove any flash hole burrs on the inside of the brass case. This can help drop pressure and help with primer ignition along with more consistent accuracy in some cases.
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    I found out how to test the primers performance once by accident. Forgot the powder.
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    Tools are available to ream out the primer pockets to a uniform size and depth. There are also tools to uniform the flash holes to remove internal burrs. Most commercial brass have flash holes punched, rather than bored, and the result is internal burrs inside the case which may disrupt the shape of the primer flame and may affect how the powder is ignited. When shooters are trying to get their 100 yard groups to print smaller than 1/2", they will go to extremes to uniform everything they can.

    I use both these tools on brass for my bolt action rifles. I do not bother using them with my auto loader brass. And one day, if I have a lot of time on my hands, I may perform these procedures on my lever action rifle brass.

    This is wasted time and effort for handgun brass. I don't bother. (I pick up range brass also.) Nor do I bother sorting handgun brass by manufacturer. Regardless of preparation or sorting, handgun ammo is capable of shooting into 1" at 15 yards, which if a lot better than I can shoot it. The benefit to uniforming the primer pockets and flash holes on rifle brass may reduce your 100 yard group sizes by up to 1/2"--or maybe not.

    I have thousands and thousands of rounds of handgun brass in multiple calibers. The uniforming process becomes tedious after about a hundred. For my rifle brass, I've only got several hundred per caliber--an order of magnitude difference in effort.
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    And then there is the 45ACP brass that takes small pistol primers.
    ..

  11. #10
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    HiKayaker nailed it, the flash holes used to be drilled back in the day, but the factories switched to using punches in the last couple decades to reduce tool wear and replacement time. As the punches wear they tend to bend and/or flatten out, and the holes get bigger, change shape, and become oblong.

    Another reason for flash hole irregularities is that the factories have been experimenting with new priming compounds, with altered burning characteristics (known as "brisance") and some compounds burn hotter, or faster, or longer, and the flash hole size is changed to suit the characteristics of the new primer. 45 fans are still grumbling about the fact that CCI/Blazer started using SMALL pistol primers in a round that had used large primers exclusively for 100 years, now they had to be sorted when it came time to prime them, especially if you were using a Progressive press. Some folks swear by the smaller primers for better consistency, other folks swear at them for the added step in the reloading process. I prime off-press, so if I'm priming LP primers and grab a case with a SP pocket, I just toss it in a bin and prime those cases separately. That explains why I have two RCBS priming tools, the ones with the square primer container, so I don't have to switch things out when changing primer sizes, I just grab the other one.

    In 30+ years of reloading, plus shooting up tons of training ammo at the PD, I've pretty well seen it all. Rounds with huge flash holes, some with none at all, some with no powder, even bullets seated backwards. I no longer believe that "Each rounded carefully inspected by hand" nonsense, I'm betting the inspectors see about a thousand rounds a minute go by, and they're lucky to catch any flaws at all!
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