In peacetime, it is possible to get court-martialed if you drop or lose your weapon. But during combat, that rarely happens because equipment loss is expected and planned for so getting a replacement is much easier.

I know soldiers drop their weapon in combat for the following reasons:

When it jams; especially when the soldier can’t clear the jam
When the weapon gets damaged
When the soldier runs out of ammunition
When the soldier experiences some kind of mental episode
When the soldier is injured or wounded
When the soldier is surrendering
During peace time, when the National Guard unit I commanded had a small group of men performing a task that required deep concentration, it was difficult for them to keep an eye on their stacked weapons. And we had a battalion master sergeant who loved to walk around to search for and confiscate unattended M16 rifles. So to help this small group of my men, I would sling all of their rifles on my body because I could not stay in one place just to guard them. It was strange to see me walking around carrying up to six M16’s at a time (2 on left shoulder, 2 on right shoulder, 2 across my back in an X formation). When our battalion executive officer saw me do this for the first time, he began calling me “killer”.

culled from quora