The most common and most likely answer to this crossword clue is the 6 letter word SIGHTS
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "Things seen/on guns" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case things seen/on guns = sights.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SIGHTS mean?
SIGHTS noun- (in the singular) The ability to see.
- The act of seeing; perception of objects by the eye; view.
- Something seen.
- Something worth seeing; a spectacle, either good or bad.
- A device used in aiming a projectile, through which the person aiming looks at the intended target.
- A small aperture through which objects are to be seen, and by which their direction is settled or ascertained.
- A great deal, a lot; frequently used to intensify a comparative.
- In a drawing, picture, etc., that part of the surface, as of paper or canvas, which is within the frame or the border or margin. In a frame, the open space, the opening.
- The instrument of seeing; the eye.
- Mental view; opinion; judgment.
- To register visually.
- To get sight of (something).
- To apply sights to; to adjust the sights of; also, to give the proper elevation and direction to by means of a sight.
- To take aim at.