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Thread: .30 v .303

  1. #1
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    .30 v .303

    The only .30 caliber rifles I own are .303 British, & have always used Hornady .30 caliber gas checks. Looking at Pat Marlin's Checkmaker list of sizes available I see he shows both .30 & .303, what is the difference?
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    Boolit Grand Master

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    .30 cal. bullets are typically sized to .308 or .309 dia. (7.62 mm bore diameter)
    The .303 is more like .312-.314. (7.7 mm bore diameter)

    The .303 gas checks will fit better for the slightly larger bore diameter & boolits for it.
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  3. #3
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    Designed for .308" groove diameter barrels verse .311" groove diameter barrel would be my guess but send him an email to get 100% correct info.
    Last edited by M-Tecs; 11-24-2021 at 10:36 PM.
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    Quote Originally Posted by bonza View Post
    The only .30 caliber rifles I own are .303 British, & have always used Hornady .30 caliber gas checks. Looking at Pat Marlin's Checkmaker list of sizes available I see he shows both .30 & .303, what is the difference?
    "what is the difference?"
    About .003"
    But, that all depends on your boolit mold and the diameter boolit shank is makes on your boolit.
    Typically it's close enough to use same GC.
    https://castboolits.gunloads.com/sho...-vs-Shank-Size
    If you are having issues installing a Homemade GC, changing the material thickness can sometimes solve the problem.
    Another thing that can be done, is to change your alloy or casting technique to alter boolit shank diameter.
    That's my 2˘
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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check