"Jessie removed the small revolver from David's head when he heard the screen door open downstairs. He stared at David with wide eyes and a scowl. David shrugged his shoulders and shook his head."
Me three about seeing Jesse literally extract the gun from David's head!
And as someone points out, revolvers are more or less of a size; it's only significant if it's, oh, say, a pocket Derringer hardly larger than your thumb. (In which case, say "pocket Derringer".)
So I'd revise it:
Jessie pulled the revolver away from David's head when he heard the screen door open downstairs.
The first line, with minor tweaks, is a good hook. But I agree with someone who said why not dialog next, so we have something more personal than staring and shrugging?
But I might actually do something entirely different:
Jesse put the gun to David's head. "So this is it."
Downstairs, the screen door slammed.
Jesse jerked the gun back.
"WTF?" said David.
Jesse said, "How should I know?"
Well, nonsense dialog here (obviously it needs to relate to your story) but you get the idea.
I do think it's an interesting place to start.
ETA: as someone notes about the spelling of Jessie... my fingers altered it to "Jesse" without consulting my brain, which I suppose goes to confirm that.