Model/Pattern (relating to weapons)

Countries throughout the world use single-letter abbreviations for model, pattern, or a translation therefor (e. g. M-16). What are the Latin translations for model and pattern for this usage of the words? If that weapon's been refined since original issuance, it will have an A, representing something akin to alteration, (e. g. M-16A1). What's a good translation for this usage of alteration?