It's a double. I think 311A is the Stevens number although it is on the JC Higgins gun.
Here is my problem. If you look at the 311 in Gunparts Catalog they show a screw in the front and rear of the trigger guard. The one I have has the front screw brazed in or cast in and threaded and I guess you put it on by turning the whole trigger guard and when in place secure the rear screw.
Anyhow, the front screw is broken. I can't figure any strong way to fix it that looks nice. would be great to get the correct guard.