Full Metal Jacket Version Quaffer.
This is my Rifle,
This is my gun,
This is for fighting
This is for fun.
Dad learned his version during WWII. He died in 1975 and Full Metal Jacket came out in 1987. It just goes to show you, things change. He probably told me that in 1969 so it may well be my memory that paraphrased the couplet. Of course if you polled four different drill instructors you'd probably get four or five different versions.
Even now I doubt any military has much tolerance for calling a personal weapon a "gun". Having your own vernacular for things separates members of your organization from the rest of the world. It builds unity. If you know the "right" words for things "you" are one of "us". It's true in any field you care to name.