Model 12-A UhOh!

[umcpumpgun]

The size doesn't sound exactly right unless it broke in half and fell out,but it may the part refered to as the retainer. It is a little long(around a couple of inches long and about 1/8" wide and pretty thin)flat skinny peice that fits between the barrel and mag. tube immediately in front of the receiver. Normally the forearm and action bar and mag tube has to be taken out for this to come out unless it broke in half. Your gun will dry cycle fine without it,but ctgs. will go everywhere when you try to cycle a live round. Look in the small gap between the mag tube and barrel immediately in front of receiver and see if can spot whether or not it is missing. Hope this helps.

[DavidFagan]

Might want to check the gallery there is a model 12 / 121 with parts list, service manual, etc

http://www.remingtonsociety.com/gallery ... temId=3770