which model is your gun? You've listed most all the necessary info needed to tell except what the barrel length / number of shells it holds.
From the mossberg website:
590A1 - 12 Ga., Heavy Barrel, Clean-out Tube, Metal Trigger Guard
& Metal Safety, Parkerized finish
Catalog # Stock Barrel Choke Cap.
51410 Speedfeed 18.5" Bead CYL 6
51518 Speedfeed 18.5" GRS CYL 6
51668 Speedfeed 20"GRS1 CYL 9