[DDGator]

I have an 870 Wingmaster that was a police trade in.

I want to buy a replacement magazine cap with a sling swivel from Brownells (made by Michaels of Oregon).

There are two for the 870 -- one for guns with an Internal Tube Rachet and one with an Extenal Tube Rachet....

How do I know which I have?

[dfariswheel]

Remove the magazine cap.

If you have an Express gun, you'll see a green plastic plug inside the magazine tube with coarse "teeth" in the middle.
This would be an "internal ratchet".

If you have a Wingmaster or Police gun, remove the cap, and you'll see a ring of dimples around the outer rim of the cap, and there'll be a small spring loaded ball on the front of the barrel's support ring.
That is an "external ratchet".

[DDGator]

External! Thanks!