The Below could be called my work, but it is based off of 20+ years of reading BattleTech Source books, rule books, and novels.
Real World Equivelencie
For the most part the BattleTech Machine Guns are based off of Machine Guns and Mini-Guns of the Real World. If a manufacturer and calibre is cited, and there is a real world weapon with the same or similar nomenclature, then you have found the real world stats for the weapon.--Cameron 19:44, 17 June 2010 (UTC)
Premis: The RPG is the means that real world weapons have been passed through into BattleTech.--Cameron 19:44, 17 June 2010 (UTC)
First it is necessary to determine the Area of armour that would be affected in square mm. (a 7.62 mm diameter circle for .30 calibre or 7.62 mm shells). Then you would need to figure out the number of joules that would be applied to each mm (so total Mega Joules divided by the surface area). With this you would look at the real world information in regards to World War II spec Rolled Homogeous Armour and determine what the depth of penetration would be for a shell with the required characteristics. Note, RPG AP of 5 means that the shell has a 50% chance of penetrating a stated thickness of Rolled HomoGenous Armour Equivelent (RHAe), say if a Real World Shell is .50 Calibre/12.7 mm and is stated to have a 50% chance of penetrating a given thickness of armour at a given distance... then most of the variables in the formula for BattleTech damage has been filled in for you.
Number of Damage Dice= x = 5
Average result of d6= Value = 3.5
Armour Penetration Value = AP
Barrier Rating of Target Armour = BAR
Depth of RHAe Penetration = P in milimeters
Diameter of Shell/Impacter = D in milimeters
Mass of Shell/Impacter = Mi in grams
Mass of RHAe penetrated (Cylinder) = Mc in kilograms
Mass of RHAe penetrated (Plate) = Mp in kilograms
Surface Area of Plate = A in mm, generally 5 sq meters for vehicular armour
--Cameron 19:44, 17 June 2010 (UTC)