The butt plate screws (2) at the end of the stock must first be removed. You will need a long shank flat tip screwdriver to remove the screw at the bottom of the center hole in the stock butt. Reverse to reassemble.
Get a copy of the Gun Digest Shotgun Assembly/Disassembly manual. It should have the Mod 67.
You will need the help of a gunsmith
Best left to a trained gunsmith.
Take it to a qualified gunsmith to find out for sure. Sounds like it could be a problem with an extractor or spring.
To take apart a Stevens Model 311 double barrel for stock replacement, first ensure the shotgun is unloaded and the safety is engaged. Remove the forend by pushing the release lever and sliding it off the barrel. Next, locate the stock screw at the rear of the receiver, unscrew it using an appropriate screwdriver, and then gently pull the stock away from the receiver to detach it. Be cautious to avoid damaging any internal components during this process.
It's a .410 bore shotgun
Your shotgun was made for Sears by Stevens, and is their model 311. It should take 2.5 inch and 3 inch .410 shells.
Take it to a professional
Take it to a gunsmith
A basic price guide on the pre-64 model 1894 rifles is between 350-550 dollars.If your rifle has any special order features such as checkered stock,half magazine,shotgun style butt stock,take down model etc.With a better than average finish on the wood and metal,we could be talking over 1,000 dollars.
Remove the butt plate on the shoulder stock, at the bottom of that big hole is there's one big screw flat head that holds the stock to the receiver. There may also be a single wood screw at the very end of the lower tang as well on some models.
The Western Field model 30 pump action shotgun and the Stevens model 520 shotgun are one and the same firearm.Savage/Stevens made these for Montgomery Wards.The shotgun in question should show that it was chambered for the 12 gauge shotshell.The length of these shotgun shells were 2 3/4in. If your shotgun is not marked,I would have a gunsmith make a quick check of the chambering for you.This will only take a couple of minutes to do.