the internet
Not enough information.
Owners manual, Gunshop, most rifles have the caliber listed right on the barrel
Contact Polards.
None published. Try shotgun collectors.
Local stores that sell guns or weapons will have a variety of information for an consumer with questions about sniper rifles. Academy and Wal-Mart are two different providers of guns and weapons who also sell sniper rifles.
There's a whole shelf of books on firearms in your library. Or you may find information on www.savagearms.com
Look up the Marlin shotgun with the same model number.
Any good sized library will have books on firearms and how they work.
ESSEX Tradename used by Belknap Hardware Company of Louisville, Kentucky on shotguns made by Crescent Fire Arms Company. ESSEX Tradename used by J. Stevens Arms Company on rifles and shotguns.
May not have one- not required by law on rifles and shotguns until 1968.
Impossible to answer without knowing who made it.