Interesting, this scene.
I’ve seen comments about parallels to John in Lester here, but…look at him with that gun.
Martin somehow conveys that Lester is not comfortable with a gun, at all. He looks awkward with it, the gun is leading him, not the other way around.
When he’s playing John with a gun, John looks utterly comfortable with it. Think of the “gun vs. bike” bit in TGG, or the Dewar’s Hollow scene. The gun is an extension of him, it isn’t an object he’s holding.
Both are very effective bits of subtle physical acting, and make it clear that Martin chooses his gestures and body language carefully. It’s even more striking when one considers that Martin himself is probably NOT super comfortable with a gun - he doesn’t seem like the sport-shooting type - so the fact that John looks so at ease with his is a job well done.