Well, it looks for all the world like a Remington grade 1 1889.

Lloyd thanks for the effort in providing the pictures. If you could, take another look at the gun. When you open it, there should a serial number stamped on the receiver. Also, when you take the fore end off there is a serial number. Do they match? Would you post them?

If you have a mic, open the barrels and measure across the chambers. What is that measurement? If you don't have one, do have some 20ga shells? Check to see how one fits in the chamber. Do NOT fire the gun with that shell. If this an older gun that has been restored in some way, it may not be safe.

Pete