Point blank range

Pick a vital zone — say 8 in for deer-sized game — and imagine a horizontal tube of that diameter centred on your line of sight. Tilt the barrel up until the bullet's arc just kisses the top of the tube at its highest point. The distance from where it first enters the tube to where it finally drops out the bottom is your point blank range, and the far crossing of the line of sight is your optimal zero.

• Vital zone — bigger zone, longer window, but a bigger allowance for error you may not want to spend.
• Sight height — a tall scope mount pushes the near edge of the window further out.
• Velocity and BC — a flatter load stretches the window; they matter far more than cartridge name.

MPBR trades precision for speed. It is excellent for walk-up hunting where a shot appears at an unknown distance and you have no time to range and dial. It is the wrong tool if you shoot from a rest with a rangefinder and a turret, or if you shoot small targets — a 4 in zone gives a much shorter window than most people expect. In those cases a known 100 yd zero plus dialled corrections from a DOPE card is more precise at every distance.

One flat-launch trajectory is integrated, then the launch angle is applied as a linear tilt of the sight line — which is accurate to well under a click at these angles. The steepest tilt that keeps the whole path inside the zone is found analytically, and the near zero, far zero, maximum rise and the resulting 100 yd point of impact are read off that path. Sight in for that 100 yd figure and you have your MPBR zero.

Run your own numbers on the point blank range calculator.