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The 520s are my all time favorite shotgun and I've put a few of em together. I can tell you it's not unusual at all for the shells in the magazine the rest on the lifter and not the shell stop. The lifter springs have a few different styles, single and double leg, and if you get on you may have to subtley bend or modify the spring to get it to work with your gun. Your 520 is the older one, it's not the very first pattern but it's close. I'll try to remember to get mine out when I get home and post more info, I have a 520, model 30, and 520A.

 

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Musser13,
The Model 520 (79013) will have an A suffix to that number and is from around 1922.

The Western Field Model 30 (1309), a store brand Model 520, should have either a C suffix or a U prefix. A “C” gun would be from around 1933 and a “U” gun from around 1935.

Internally these guns are very different. The earlier one has a recoil block in the left side of the receiver and doesn’t unlock after a dry fire. The later gun has the coil spring you noticed that does away with the recoil block by putting pressure on the slide lock release.

I don’t have access to my notes and guns at the moment but I believe both shotguns should use the double lifter spring, the single spring is for the later Model 520A (1940-1949). Can’t remember exactly.

Jack First gun parts is the best source for remanufactured lifter springs.

Here’s a history of these shotguns that I wrote a few years ago that will answer some questions: https://www.gunvaluesboard.com/stevens-520-and-520a-identification-guide-2617.html

I know that the 520A does definitely use the single leg spring, I had to fix that on mine, I'll have to check the 520 and model 30 when I get home. I never knew that later versions can unlock on a dry fire, I though none of the would because of how the shotgun is inertia locked when in battery. I don't think my 520A unlocks on a dry fire, was it just the Model 30 that does that?