Your shotgun appears to be a Mossberg, made between 1948-85 variously as the Model 183, 184, 283 & 284, with each numeric model having two or more alpha sub-models (A, B, C, etc), made with either a 2 or 3 shot magazine in .410 only.
Other gauges, and the .410 single-shots, had a different series of model numbers.
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