Take it to a gunsmith
Take it to a professional
what is the market value of a remington 20 gauge semi-automatic sportsman 58 shotgun?
75-400 USD
50-200 usd
First of all you have the "sportsman 48", "sportsman 58" and the "sportsman". If it is a plain sportsman it's value depending on it's condition is from 150 to 200 dollars.
Your question answers itself.
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About 275 in good condition
If you look closely, I think it's a Sportsman 48 instead. Anywhere from $100-$300 depending on condition and options.
50-500 USD depending on specifics
Try e-gunparts.com, Shotgun News, Gun List, local gun shop, gun shows.
If shotgun is in good working condition and no rust or cracks, then it would have a value of between $225 - $300.