I have a winchester model 1873 38/40 serial 1394434. When would it have been manufactured?

Like Vangion said it doesn't appear in their data base. Here's a site to check it out.

http://armscollectors.com/sn/windates.htm

Are you sure it is a Winchester?

Are you sure it's an 1873?

The number does not exist in the Winchster database

But it does coincide with a model 1894 made between 1943 and 1948

Your model 1897 was made in 1898, according to the serial number records that remain. The value can range from $75 for a common 12 gauge field model in poor condition to $3000 for an excellent condition black diamond trap model. The most common were field grade guns in 12 ga., typically they came with a 30" barrel, full choked. The "bluing" finish on the metal is usually worn off the early ones or, if they were stored for long periods of time, it has turned to a brown 'patina'. With the original stock and forestock free of cracks, these are worth approximately $400 in good condition. Add $100 for 16 ga. Add $200 if in like new condition. Riot/police models are worth an extra $200 (look for 20" barrel and metal buttplate). Military "trench" models are worth an extra $400 - 800. Solid frame versions (as opposed to the later take-down design) are worth an extra $100. Beware of fake riot, trench, and trap models.

Check here for information.<> rare winchesters.com....