Re: Value Model 311D 16 Guage Shotgun
Those usually run about $200-250 or so in average condition, but if it is like new, $300 would be about right. Those guns have no collector value; they are utilitarian hunting guns.
Up to the last part of 1968, serial numbers were not required by law and many inexpensive guns made before that don't have them. There is no problem if there is none.