Came across a brief review of the Diana 460 Magnum and the reviewer
stated the 350 M has a 5" stroke, the 48/52/54 has a 4" stroke and
the 460 M has a 4.5" stroke. Also stated the 460 M has the same size
bore/piston seal. Then mentions the 460 M has a portless sliding
cylinder and the 350 M and 48/52/54 don't and that this feature
enhances the 460 Ms performance.

I assume he means compression tube when he types/states cylinder
but I'm kinda puzzled by this portless thang. Portless?! Man I haven't
looked yet but I know there's gotta be a hole, a transfer port, a
release or exit for the air. I'm not making sense of this portless
business yet! Help me figure it out.

Prehapz he meent Loadink Port fer de pellet

that doesn't make any sense. Maybe he doesn't mean compression chamber when he says "cylinder"?

Can you post the link to this review?

very short transfer port. That's it!