This Remington manufactured late variation 28" plain barrel with a factory modified choke is for the model 11-48 semi-auto shotgun in 16 gauge with a serial number above 5,509,000. This barrel is in very good condition retaining the mojority of its thinning original blue finish blending with a brown patina and having a few spots of rust.  (file photos)

Note: Remington model 11-48 semi-auto shotguns with the following gauge and serial numbers have been observed with this part:

16 Gauge: 5522646 & 5529102