This closely parallels interior ballistics but expands upon that by including the condition of the cartridge case in obturating the propellant gases. and clearing the firearm in ejection; and the condition of the projectile in terms of such things as structural integrity, and sabot petal discard.
LTC Alphin has done some very important work in this area. Among other things, this work focused on the differences in the A-131 and the A-129 call-out on 7.62x51mm NATO ammunition. Some ICB (Idiot Civilian Bureaucrat) decided that some money could be saved by thinning out the cartridge case wall on the ammunition because the M-60 machine had a “soft” cycling stroke. But the M-73 family of co-axial machine guns for the M-60 tank family had a more abrupt cycle and the ammunition failures damaged guns and made them useless. LTC Alphin created a work around that allowed the ammunition to be consumed in training. Ammunition function also addresses the cartridge in charging the magazine (in repeating firearms) and feeding from the magazine into the chamber.
LTC Alphin’s skills as an Ammunition Function Expert, coupled with skills as a Firearms Manufacture Expert, directly led to the exclusion of bogus firearms ammunition “evidence” and the resulting dismissal of all charges in the Holmes case. During his time running the testing at Jefferson Proving Ground, LTC Alphin’s ammunition function expertise led not only to improved data capture and increased through-put (a nine fold increase of volume) but also led to the solution of the 4.2 Inch Mortar crisis.