Dean had a very invasive, but systematic way of cleaning all their weapons at one time. It was something he did once a week, and something Sam found sort of fascinating to watch. First he put towels down on Bobby's desk (even though it was so scarred up that Sam doubted Bobby would notice). Then he took each of the guns, starting with the smallest ones. He would take them completely apart. With wire brushes and polishing cloths, he would return them to a dull, matte gleam. And then he would reassemble them, as efficiently as he could.
Dean would glance at the big clock on Bobby's wall as he did this, timing himself, like an old habit he couldn't shake. Sam remembered their Dad with the gray stopwatch. "Dean… go!" And Dean's fingers would make swift work of clips and firing pins, so fast that it sometimes looked like magic. But it was never quite fast enough. John Winchester said it wasn't good enough for the Marines.
Watching him reduce them to their components always made Sam forget that he thought guns were base, violent things. Dean didn't think so. Dean admired a nice gun the way Babe Ruth would speculatively slice the air in front of him with a new Louisville Slugger, the way Jimmy Page would carefully adjust the strings of a Gibson Les Paul.
It must've been very satisfying in its way to him: everything snicking, clicking, snapping and sliding into place, when so many things about their lives were the opposite.
Sam thought of the weapon maintenance as the closest thing Dean had to a Zen exercise, his monthly tune-up of the Impala the other.
Dean liked when things worked. He liked getting his hands dirty. His fingers would bluntly explore over tangible things that had a specific purpose and no ulterior motives. It was the same way a musical prodigy might rest their fingertips on the bow of a violin, taking in some kind of sweet Braille that Sam could only appreciate as an observer.
Sam had sat alongside and talked to Dean when he was under the Impala, trying to make repairs. Dean would work until he was black with grease, sweat-soaked, fingers bloody, cursing wildly and talking to inanimate parts like they had insulted Mom. He sang to himself when the repairs were going well. He wouldn't realize until later that he'd hurt his back, or sprained his wrist. He was in the moment of the thing, his whole body lost in the hum.
Sometimes Sam didn't say anything. He would just sit there and have a beer while Dean toiled away, ready to hand him wrenches, listening to him sing.