Warning, sarcasm ahead...
Ignore DanV, if you show up for a test in your underwear there's no way they'll promote you to sergeant, much less make you a sniper!
...End sarcastic message
Honestly, I think DanV makes a good point. Muscle memory is important and dry-firing makes for good practice. When I did my brief competitive air rifle shooting in high school I liked going through my shooting positions at home to get my body settled into where it needed to be. Even now, just before I'm going to the range or out to hunt I like to get the weapon(s) I'm using and move through shooting positions with them. It seems to help me get my mind set on what I'll need to do.