I have a stevens 311 with no serial numbers.How can find out

I think I can confuse you a little. For starters , no serial number, then it was made prior to 1968. After 1968 serial numbers were required on all firearms. If it was made prior to 1949, then no joy. However from 1949 to 1970 Stevens used a date code on all of their double barrel shotguns. It will appear as a small circle with a letter and number. It should be found behind the hinge pin or ahead of the trigger guard on the bottom of the shotgun. A = 1949 thur X = 1970, O and Q are not used. Let us know if that helps.

I found a circle with the letter H.It's under the barrels when you break it open to eject the shells.This makes it a 1956 year right?

I looked in the wrong place.It has a 6K.

It's on the bottom at the hinge pin.That makes it a 1959 right.

Right on the money, K = 1959, Hey that was easy. Good luck and shoot safe.