A serial number in the 300,000 range would make it a model 1900, model 1894's had serial numbers in the 100,000 range. The biggest difference between the two models is the '94 has a Purdey style forend latch and the 1900 uses a Baker style snap on latch similiar to the Trojan. Dave Noreen knows quite a bit about Remington doubles hopefully he will come along soon and give some more insight.
Some information Dave posted awhile ago on the Remington forums:
http://www.remingtonsociety.com/foru...php?f=7&t=2491