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Thread: 30 cal Gas Check Shank Size

  1. #1
    Vendor Sponsor thehouseproduct's Avatar
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    30 cal Gas Check Shank Size

    I am looking to honcho a group buy for a 30 cal Mihec mold. It is a gas check design and buyers want 2 different diameters. 316 and 311. Since the mold makers use a shaped end mill to interpolate the cavity, the gas shank diameter will vary by 5 thou as well. If target the 316 version to have a 0.283" diameter gas check shank, will 0.278" be too small for the 311 version?

  2. #2
    Boolit Master turbo1889's Avatar
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    Some "fat 30-cal" molds like used in 303-brit have oversize gas check shanks measuring up to 0.290" diameter notably the molds made by that mold maker I can't remember the name of down in Australia.

    Long story short, I think you are probably better off making the smaller diameter 0.311” boolit with the 0.283" gas check shank and letting the larger size molds have an oversize shank diameter.

    In addition a slight taper to the shank (slightly smaller diameter at bottom of shank then at the top) is usually a good idea for ease of check installation especially for when the shank is oversize for the oversize mold diameters.

    Go to Ranch Dog’s web-site and take a close look at the dimension diagrams for some of his gas checked molds to see what I am saying about the gas check shank having a slight taper to it and being slightly oversize for "fat 30-cal" sizes. A notable example is his 32-20 boolit design where the shank starts out at 0.284" at the bottom of the shank and then tapers up to 0.288" at the top of the shank thus basically a shank that works like a wedge to open up a standard size gas check to slightly larger diameter in order to match the slightly larger diameter of the boolit compared to a standard 30-cal diameter range. In comparison his standard 30-cal diameter boolit for the 30-30 lever action starts out at 0.281” at the bottom of the shank and then tapers up to 0.285” at the top of the shank.

    Long story short, you are probably best off using a shank with a slight taper to it and making the shank just slightly undersize for the 0.311 diameter boolit so that the bottom diameter of the shank will just barely squeeze into a standard gas check internal diameter in the larger 0.316” size and then the taper of the shank opens it up slightly as it is seated.

    That is my $0.02 but you should realize that I have never been a group buy mold purchaser and just design my own molds and pay the extra price margin for a “one off” straight from a custom mold cutter rather then going with a group buy mold. You should probably check with the guys who do a lot of group buy mold buying and see if the solution I suggest rubs them the right or wrong way.

  3. #3
    Boolit Master JIMinPHX's Avatar
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    If you have the cherry sized so that it cuts an undersized gas check shank for the smaller mold cavity diameter, then you can open up the GC shank later by plunging a reamer or end mill. I am not aware of a way to reduce the GC shank diameter after the cavity is cut. Enlarging it is not that tough.
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  4. #4
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    Are the shanks tapered at all? It looks like some are, and others aren't.

  5. #5
    Boolit Master turbo1889's Avatar
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    Quote Originally Posted by thehouseproduct View Post
    Are the shanks tapered at all? It looks like some are, and others aren't.
    Correct !!! ~

    Some mold makers make their molds with straight shanks and some taper the shanks. The benefit of tapered shanks being that when done correctly they allow the check to still fit over a wider range of tolerance in both the mold cutting operation and across different casting alloys. Obviously, the benefit of straight shanks being that they are simpler to manufacture.

    JIMinPHX by the way is absolutely correct in his answer being to make the check the right size for the 0.316" diameter on the cherry cutter and then ream out the check shank to the correct size on the smaller 0.311" diameter cavities. The question of course being whether or not your mold cutter is willing to do the second step or not. A tapered shank is the only way I know of doing it in one step operation across a range of diameters with a single full profile cutting tool such as a cherry cutter and not making a second cut.

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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