Ballistics Dimensions and Definitions



Handgun Dimensions



    Caliber: .38 Special
    • S&W Model 36, Double action, 1-7/8" barrel, 5 shot, manufactured 1960
      • OEM Trigger Spring and Hammer Spring
      • Trigger pull (double action): 8 lbs 8 oz
      • Trigger pull (single action):  2 lbs 14 oz
      • Cylinder chamber: 0.xxx" each
      • Cylinder throats ~0.xxx"
      • Barrel slugged: Bore across lands 0.xxx", Groove dimension 0.xxx"
      • Starline brass mouth diameters (RCBS dies)
        • After firing: 0.xxx" ID, 0.xxx-0.xxx" OD
        • After resizing: 0.xxx" ID, 0.xxx" OD
        • After expander: 0.xxx" ID, 0.xxx" OD

     Caliber: .44 Magnum
    • Ruger Super Blackhawk, Single action, 7.5" barrel, 6 shot, manufactured 20xx
      • Wolff Trigger Spring and 18lb Hammer Spring
      • Trigger pull: x lbs x oz
      • Cylinder chamber: 0.xxx" each
      • Cylinder throats ~0.xxx"
      • Barrel slugged: Bore across lands 0.xxx", Groove dimension 0.xxx"
      • Remington brass mouth diameters (RCBS dies)
        • After firing: 0.xxx" ID, 0.xxx-0.xxx" OD
        • After resizing: 0.xxx" ID, 0.xxx" OD
        • After expander: 0.xxx" ID, 0.xxx" OD

    Caliber: .45 Colt
    • Ruger Blackhawk, Single action, 7.5" barrel, 6 shot, manufactured 1973
      • Wolff Trigger Spring and 18lb Hammer Spring
      • Trigger pull: x lbs x oz
      • Cylinder chamber: 0.4885" each
      • Cylinder throats ~0.456"
      • Barrel slugged: Bore across lands 0.4415", Groove dimension 0.450"
      • Winchester brass mouth diameters (RCBS dies)
        • After firing: 0.4565" ID, 0.477-0.478" OD
        • After resizing: 0.449" ID, 0.468" OD
        • After expander: 0.4495" ID, 0.468" OD
      • Ruger Blackhawk, Single action, 7.5" barrel, 6 shot, manufactured 2017
        • Wolff Trigger Spring and 18lb Hammer Spring
        • Trigger pull: 2 lbs 5.5 oz
        • Cylinder chamber: 0.483" each
        • Cylinder throats ~0.4505" (0.451" bullets do not push through)
        • Barrel slugged: Bore across lands 0.442", Groove dimension 0.450"
        • Starline brass mouth diameters (RCBS dies)
          • New brass, unsized: 0.452" ID, 0.474" OD
          • After firing: 0.450" ID, 0.469" OD
          • After resizing: 0.448-0.449" ID, 0.467" OD
          • After expander: 0.451" ID, 0.472" OD
      • S&W Model 25, Double action, 6.5" barrel, 6 shot, manufactured 2017
        • Wolff 13lb Rebound Spring and Power Rib
        • Trigger pull (double action): 8 lbs 8 oz
        • Trigger pull (single action):  2 lbs 14 oz
        • Cylinder chamber: 0.483" each
        • Cylinder throats ~0.452" (0.4515" bullets drop through)
        • Barrel slugged: Bore across lands 0.445", Groove dimension 0.451"
        • Starline brass mouth diameters (RCBS dies)
          • New brass, unsized: 0.452" ID, 0.474" OD
          • After firing: 0.457" ID, 0.479" OD
          • After resizing: 0.xxx-0.xxx" ID, 0.xxx" OD
          • After expander: 0.xxx" ID, 0.xxx" OD

        Rifled Barrel


         The bore diameter is the minor interior diameter of a barrel that is the diameter of a circle formed by the tops of the lands. It is the distance from land to land.

         The lands are the area of the barrel not machined out when rifling.

         Grooves are the spiral cuts from rifling the barrel.
        The groove diameter is the diameter of a circle circumscribed by the bottom of the grooves.

         Caliber in the US is normally expressed as groove diameter, while the bore diameter is normally expressed as calibre (land to opposing land dimension) outside the US.




        Fired bullets display the alternating bands of the lands that cut into the bullet. Grooves in bullets may appear as unblemished for bullets with diameters smaller than the barrel groove diameter. Lands in bullets appear as striped depressions where the bullet metal was compressed or cut by the barrel lands.


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        Bullet Performance


        Bullet performance at the target depend on multiple, often uncontrolled, factors. Rules of thumb for handguns are:
        • Good performance requires a bullet to closely match the groove diameter of a barrel to ensure a good gas seal and hence maximal bullet propulsion.
        • Adequate pressure (~powder charge) is required to obturate a bullet to seal gas from escaping around the bullet in the barrel.
          • Bullet diameter should be a slip fit through revolver cylinder throats.
          • The ideal cylinder throat diameter is about one half a thousandth (~0.0005") over the maximum groove diameter of the barrel.
          • Loads which match your particular gun will give the best possible performance.

          • Lead Bullets: (Ref: http://www.shootingtimes.com/ammo/ammunition_st_lowdownleadfoul_201002)

            • Good lead bullet performance in revolvers depends on the chamber throats not being too much larger than the barrel’s groove diameter. Lead bullets should be 0.001" larger than the barrel groove diameter.
            • Low-pressure or under-diameter revolver loads can cause serious blow-by leading.
            • Chamber throats that are no more than 0.002 inch over groove diameter, can provide decent accuracy and minimal leading with bullets sized = or > throat diameter.
            • Cast bullet sizes that generally are preferred for properly sized cylinder throats:
            • 38 Spl: 0.359"
            • 44 Mag: 0.430"
            • 45 Colt: 0.452-0.454"
            • Large barrel groove diameter (> throat diameter) leads to hot gas leaks around bullets and poor performance.

          (Source: http://www.shootingtimes.com/ammo/ammunition_st_lowdownleadfoul_201002)



          Precision and Accuracy