mossberg 500 w/ 20" barrel
Mossberg makes a 500 with a 20" barrel with the 7 round factory mag (so that's 7+1)
You won't be able to switch our the barrel because of the position of the ring, but it puts the ring right at the end of the 20" barrel, hence the long factory mag
I got mine at Big 5 a couple months ago for about $270 + background check + taxes (plus some ammo, making it a total of about $312 out the door I think).
Screaming good deal and I'm very happy with it.
It's item no 50577 I think in the mossberg catalog