savage/stevens model 77b shotgun with 18" barrel ejection problems

I recently bought a savage/stevens 77b, love the gun, shot several rounds through it, then it developed ejection problems. It seems like the round in the feeder tube would try to feed before the spent round ejected. Jamming the action, and requiring me to field strip to get the rounds to release. Any idea as to why this is happening? My thoughts are its worn parts. The gun is pre 1964, and has no serial numbers on it so I can't really find much info. The first time it happen the ejector clips popped out of the bolt assembly. I fixed that, took it out to the range and fired several rounds through it. Seemed to work fine, then sent some OOB shot through and the problems started again. I field stripped it, fired more rounds and it seemed to work. I use this gun primarily for home defense, because of its 18" barrel, and I want to be able to depend on it.
I'm new to the forum, so any help would be apreciated.
Thanks gang.