The spelling of the word "casull" is often confused with "Casual" due to their similar sounds. However, "casull" is actually pronounced as /ˈkæzəl/ which is spelled with two "L" letters at the end. The combination of "S" and "U" letters forms the sound /zə/ while the "double L" indicates the vowel sound /æ/ to be shorter. This word refers to a type of cartridge used in guns, specifically the .454 Casull cartridge. Remembering its phonetic transcription helps to avoid misspelling the word.
The word "casull" is derived from the surname of its inventor, ArmaLite engineer David C. Casull.