I've done US drill team stuff (there are several videos of such on YouTube, including the Marine's Silent Drill Team) and while there is a lot of twirling and clacking and clicking it comes from taps on the shoes, doctored handguards, and gloved hand slaps to wood or metal. Shouldering arms puts almost no pressure on the shoulder if done right. Timing means a lot -- it's impressive to watch an officer walk between two rows of guys twirling rifles with bayonets attached, and dropping a rifle tossed back for you to catch can get you in trouble.

But slamming guns into bodies, nah. If it happens it's an accident.

This is for the US Military -- YMMV.