The build up here is quite effective and cramming a flashback into such a short story is no mean feat.

I’d almost be tempted to strip out some of the descriptive elements earlier on so that the actual verbal reveal of the gun at the end is more effective.

There’s an oft-repeated piece of advice that too many adjectives/adverbs can be detrimental to a piece of writing. I think there’s an element of that here – “This piece of rust wants to take his life” is snappier than “This unmoving piece of rust” and, to my eye, more threatening. The reader knows it is unmoving already so that word becomes redundant.

Check out this article for more on that:

http://www.wooptydo.com/?p=458

Also, it would make more sense grammatically to have “The gun lay forgotten on the floor” and I think it sounds more dramatic as well.

Try writing a similar piece of prose but with no adjectives/adverbs. You’d be amazed how interesting it could be.

Ok Thanks!
I have removed some of the unneccesary adjectives and it does look a whole lot better to me.
The last line I think I’ll leave as is, because its supposed to be continuing to be there, sort of timelessly. I don’t know it made sense in my head.

You may be right on the last line. If it makes sense in your head, chances are there’s a reason for that and I take your point on ‘lying’ getting across the idea of it just continuing to be.

Looks good!