Actually the shotgun uses 16 gauge shells i have the same shotgun
Winchester stopped the regular production of 20 gauge in 1963 and the 20 gauge magnum shell wasn't introduced for several years later.
It is marked on the barrel.
the shotgun takes a 2 3/4 shell
If your shotgun is a 12 gauge pump, then you have a High Standard Model 200 (Flite King). The standard 12 gauge shell is a 2 3/4 inch shotgun shell. It can be anything from #8 birdshot to a deer slug.
Mine is a 12 gauge pump. Chambered for 3" shell.
SHould be marked on barrel. If not, have a gunmsith check it out.
50-1000 USD depending on specifics.
The 20-gauge shell will fall into the barrel and lodge. When a properly fitting 12-gauge shell is chambered and fired, it will blow up the barrel and you will have a very bad day.
NO!!! A 12 gauge shotgun takes only 12 gauge shells. A 20 gauge shell would fall into the barrel and get stuck about half way to the muzzle. You would be in for a nasty surprise when you put a 12 gauge shell behind it and pulled the trigger!!!
One can find a shell puller for a Savage model 30 series E 12 gauge pump with 3 inch chamber through Savage directly. One can also find this item through gun auctions and classifieds.
If it's a 16 gauge shotgun, the shell length is 2 3/4 inches.
I have an earlier serial number of the same gun. It takes a 2-1/2 inch shell. Hope this helps.