You didn't mention whether it has a ribbed barrel or not, or how it is choked (both of which a factors in the value). I agree with bobbywins... 44x,xxx is correct for 1926 and for it being marked "Model 12", but if your new toy is actually 44,xxx, then it should be marked "Model 1912", and it will have a short 2-9/16" chamber in it.
$300 is a very reasonable price for a 1926 vintage plain-jane 16 gauge, and would be a real good bargain on a 1914 vintage gun. If your gun has a solid ribbed barrel, then you got it cheap!
Real Men own and shoot a Winchester SINGLE-SHOT!