Howdy, I have one of these too, it's the model 336-44 Magnum. I asked about it in several Marlin forums and here is the information I gleaned. If I knew who sent it to me I would credit them with it, but am afraid I don't recall who it was. Anyway, here it is. (and mine has never demonstrated any feeding problems.)
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.44 Magnum chambering. Manufactured from 1963 to 1967.
1963 through 1964, it's the 336-44 Magnum. This rifle doesn't have the square loop lever, it is rounded, and no saddle ring. Serial numbers would start with a W, Y, or Z.
1965 through 1967, it's the 336T. Square lever and saddle ring. Serial number would start with AA, AB, AC.