FREECHEX

Many folks are making their own checks.  A fundamental principle is forcing deformable material on to a mandrel.  I make mandrels which are the shank diameter of the nominal bullet.  For instance .281 inches approximately for th 30 caliber bullet.  Steel blocks cast different than aluminum ones.  Then the bore diameter of the rifle say .308 for the 30 caliber family measured in the grooves.  Forget about the .311-12 you size the bullets at.  The notion here is to fill the bore, seal it from the plasma of gasses, metal vapors etc.  When swaging a metal about the mandrel then half the difference of the bore(groove) diameter and the shank diameter is the theoretical  maximum thickness of the material to use as a base metal.   The first constricting forces are the die a mandrel forces the base metal through.  That will be the outside diameter of the check (OD).   Nothing will bring the check to its inside diameter (ID) of the mandrel unless the approximately maximum thickness is used.  Here, about .014” for the 7.62mm family.  Now different materials have different memory issues.  Until the material is forced or actually extruded there will be a springing back effect.  .003-005” is not uncommon.  Snugness on the shank depends on how  thick the material is to deform the base metal to the mandrel diameter. Too thin and you have krinkling like a coke bottle cap. Way too thick and you have metal weakening and elongation and thinning with little memory or spring back as a result of extrusion.  The geometry of the anvil die,and the mandrel are just a starting points.  Selection of metal and thicknesses do take a little experimenting something that this whole hobby is all about.