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Effect of flash hole size

MIKE WISKEYMIKE WISKEY Member Posts: 10,035 ✭✭✭✭
edited April 2008 in Perry Shooter Competition Shooting and Reloading Forum
I had asked about what effect a small primer flash hole would have on ammo preformance, I had a batch of brass with .055" flash holes (1st pix).Normal commercial brass has .076" flash holes. Well nobody could give me an idea of what this would do for pressures, std. dev., ect. so I ran a test on it. I opened up 1/2 of the flash holes to .076 with my flash hole uniformer and loaded 10 of each. Sat. was as nice as it gets in Wisconsin in March (sunny, 40's) so I got the coronograph out and started firing.
the brass
FLASH1.jpg
the components
FLASH2.jpg
the test equipment
FLASH4.jpg
the ranFLASH3.jpgge set-up
load, RG/90 7.62x51 nato cases, 49.0 gns. h4350, 180 gn. SMK bullets
rifle F/N M-98, Schneider 26" 1/11" barrel, McMillion stock
results
small hole; 2703 fps. ave.,38 e.s., 13 s.d. group size .480" (ave. of 2,5 shot groups
large hole; 2757 ave., 19 fps e.s, 6 s.d. groups size .315" (ave. of 2, 5 shot groups
my conclusions; larger holes=better ignition (at least with slower, hard to light powders.
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Comments

  • charliemeyer007charliemeyer007 Member Posts: 6,572 ✭✭✭
    edited November -1
    Nice setup and report. Way better than the gunrags.
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  • PinheadPinhead Member Posts: 1,485 ✭✭✭✭✭
    edited November -1
    Your tests shows about what my field experience has been for some time but went untested. My groups have been moe consistant since I started flash hole reaming all my brass; both new and used. Another thing that the reaming does is to get rid of a burrs that might be on the mouth of the flash hole and therefore create more uniformity of the flash itself. I have been told that this is totally un-necessary. However I believe that any variable that can be eleminated makes for a better load. My experience anyway. Good work Mike.
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  • perry shooterperry shooter Member Posts: 17,105 ✭✭✭
    edited November -1
    Great job .I normally like a larger sample BUT in this case you have 4 measurements to compare and all 4 show improvements with large flash hole . Here HERE well done.
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  • CubsloverCubslover Member Posts: 18,601 ✭✭
    edited November -1
    Excellent report and pictures.

    However, I thought the 22 and 6mm PPC cartridges utilized smaller flasholes and their extreme variations in velocity were very low.
    Half of the lives they tell about me aren't true.
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  • dclocodcloco Member Posts: 2,967
    edited November -1
    quote:Originally posted by cubslover
    Excellent report and pictures.

    However, I thought the 22 and 6mm PPC cartridges utilized smaller flasholes and their extreme variations in velocity were very low.


    Cubs - it is the short/fat case that allows for better ignition. If you tried to light the same amount of powder that the PPC case holds, the longer/skinnier case does not allow for a great ignition/combustion efficiency.
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  • MobuckMobuck Member Posts: 14,083 ✭✭✭✭
    edited November -1
    It has been reported that some nontoxic handgun ammo uses a larger flash hole than standard. It is cautioned that using this brass for reloading can cause higher pressures. While this is not quite what you asked about it is something to consider. The larger flash hole allows a bigger primer flash into the powder.
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  • CubsloverCubslover Member Posts: 18,601 ✭✭
    edited November -1
    quote:Originally posted by dcloco
    quote:Originally posted by cubslover
    Excellent report and pictures.

    However, I thought the 22 and 6mm PPC cartridges utilized smaller flasholes and their extreme variations in velocity were very low.


    Cubs - it is the short/fat case that allows for better ignition. If you tried to light the same amount of powder that the PPC case holds, the longer/skinnier case does not allow for a great ignition/combustion efficiency.


    Ok thanks for the clarification.

    I am always learning.
    Half of the lives they tell about me aren't true.
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