'Pull Up' Rapper Lil Mosey Not Sweating Gun Case, Surfs in Malibu

Rapper Lil Mosey has learned his lesson ... at least when it comes to surfing.

The "Pull Up" rapper doesn't seem to have a single ounce of worry as he took surfing lessons while in the middle of a very serious gun case. Surfing instructor Alex Hoffman tells TMZ ... the rapper and some friends took lessons in Malibu earlier this week.

We're told his lesson lasted nearly 2 hours ... first a tutorial on the sand where Alex taught him how to position himself on the board, paddle and then pop up on his feet. Armed with the basics, he hit the waves -- and even though he ate it, we're told Mosey did pretty well during the training sesh.

This, of course, is one helluva juxtaposition considering he's in the middle of a serious gun case. TMZ broke the story ... the 18-year-old was busted in Burbank last month after cops found 3 loaded 9mm semi-automatic pistols in the Escalade he was riding in with 3 other people.