P-Max black powder internal ballistics simulator
POWDER SELECTION
Whaling
Cannon
Saluting
Swiss No. 5,   Fg
Swiss No. 4,   1½ Fg
Swiss No. 3,   FFg
Swiss No. 2,   FFFg
Swiss No. 1,   FFFFg
FFFFFg
WARNING
Always check the relevant powder company manual or gun maker manual for maximum loads.
REQUIRED DATA
Powder weight:
 grams  grains
Bullet weight:
 grams  grains
Bullet diameter:
 millimetres  inches
Barrel length:
 millimetres  inches
EXTRA DATA FOR CARTRIDGE GUNS
Powder space:
  cc  grains of water
Case length:
  millimetres  inches
OUTPUT UNITS
Pressure output:
 bar  psi (piezo).  
Velocity output:
 metres/sec.  feet/sec.  
Energy output:
 Joules.  ft-lbs.  
    

You have missed out one or more of the parameters above.