$ calc

Field Calculator

Trajectory, maximum point-blank zero, danger space, hit probability, loophole clearance, and unit conversions, from one saved profile. The same validated solver as the terminal's calc command.

profile no rifle set: BC and MV required
sourced loads:
three saved rifles
optional
G7 for boat-tail bullets; G1 BCs more widely published
FM 3-22.10; match it to the drag model
scope center to bore center; also the loophole bore height
standard = US Std Metro: 59 F, 29.5275 inHg, 78% RH
from a Kestrel or DA card
station pressure is derived (ICAO)
if your app reports one; blank = 29.921
at your position, NOT the sea-level number apps and METARs report
blank = standard
unknown = 50 (FM 3-22.10: takes an 80% change to matter)

Saved in this browser only. The terminal's calc command reads the same profile.

full value from 3 or 9 o'clock (TC 18-32)
$calc trajectory






  

    

      
      max ordinate is half of this (GTA 07-10-004)

  

  
$calc pointblank

  






  

    

      
      

    

      
      TC 18-32

  

  
$calc danger

  






  

    

      

    

      

    

      

    

      
      Litz ABDOC115 Table 1 uncertainty presets

  

  
$calc hitprob

  






  

    

      
      scope to opening

    

      
      dialed or held for the target, not the opening

    

      
      optional: adds the clearance verdict

    

      
      schoolhouse cross-check, unofficial; ~70 M110, ~80 M2010

  

  
$calc loophole

  






  

    

      
      known target dimension

    

      
      USMC SSC0101

  

  
$calc loophole --mill

  






  

    
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  how to use
  
Profile

  
Every mode reads the same profile: drag model with ballistic coefficient, muzzle velocity, sight height, zero range, atmosphere. The preset buttons fill the rifle fields from published tables; each names its source. Three rifle slots, saved in this browser only.

  
Atmosphere

  
Enter one of: density altitude (Kestrel or DA card), altitude (station pressure is derived by the ICAO ratio), or station pressure measured at your position. The sea-level pressure a weather app or METAR reports is not station pressure; entered at altitude it produces a sea-level solution. Every result prints the atmosphere it used on its header line. Default is US Standard Metro (59 F, 29.5275 inHg, 78% RH), the assumption printed firing tables use.

  
Modes

  
    
    
  1. Trajectory: drop, wind drift, velocity, and time of flight at each range (definitions: FM 3-22.10 Table 4-4).
    2. 
    
  2. Point-blank zero: maximum point-blank zero and range: the zero whose maximum ordinate is half the target height, and the far range where the bullet falls that far below the aim point (GTA 07-10-004).
    3. 
    
  3. Danger space: the span around the dialed range where the trajectory stays inside the target height, center hold (TC 18-32).
    4. 
    
  4. Hit probability: Monte Carlo hit percentage under uncertainty in wind call, range call, rifle dispersion, and muzzle velocity (Litz ABDOC115).
    5. 
    
  5. Loophole: the bullet's position relative to the line of sight at the opening, from bore height, standoff, zero angle, and dialed elevation. The printed training-formula cross-check is the unofficial schoolhouse form; the current official formula is not published.
    6. 
  

  
Not modelled

  
Spin drift (about 12 in at 1000 m, .308-class), Coriolis (about 3 in at 1000 m), aerodynamic jump, incline. Below about Mach 1.2 drag prediction degrades; true against observed drops.





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