How the Marlin Lever Action works.
OK: This is the way this thing works,,, Cartridges are loaded thru the loading gate. Note:, that the last cartridge loaded is partially on the Lifter but prevented from going all the way on by the Cartridge Rim being forced/wedged into the notch in the loading gate. It is half on and held in place by the lifter and the loading gate.
As soon as the Lever is moved the cartridge pops on to the lifter and is pushed on to the lifter by the Magazine Spring. However it can only go as far as the Tang on the Lever that moves the bolt allows it to. The Lifter is pushing against the bottom of the cartridge and as soon as the cartridge is on the lifter and the bullet is out of the mag tube, it pops up blocking the next cartridge from coming along. Failure to do this will result in the dreaded "Marlin Jam." The way this system works allows many different lengths of cartridges to successfully feed in the gun.
The Snail Cam on the Lever is pushing against the bottom of the lifter and if it has got a Sharp Edge it will Wear the bottom of the lifter which will eventually corrupt the timing. Putting a radius on the point of the Snail Cam eliminates this problem, or more properly pushes it so far down the road that it won't become a problem for 99% of users. The last 1% (CASS guys)will have to replace the Lifter at some point.
Next, as the Lever is Closed the Lifter is forced up by the Snail Cam Pinning the cartridge against the top of the Receiver as the bolt pushes it into the chamber. This is where Wide Meplat or Stepped Boolits ran into problems. They would invariably get stuck on the Sharp Chamber Mouth as it dug into the top edge of the boolit.
Previously the back edge of the Chamber was left Sharp. As the cartridge was pushed forward the Large Meplat or Step on a SWC Boolit would catch on the sharp edge of the Chamber Mouth stopping forward progress. IE: it is jammed. Sometimes opening the Lever slightly or just shearing the offending part of the boolit off would allow the cartridge to feed. Most all Jacketed Bullets fed properly because they wouldn't get gouged into by the Chamber Mouth and their rounded Ogives allowed the bullet to pass by the Sharp Chamber Mouth resulting in a successful cycle.
Then the Trigger is pulled, the Hammer drops, the Cartridge Fires and then the Lever is cycled, The Bolt moves back and as soon as the Ejector is exposed it Ejects the Spent Case... The Hammer is cocked at the same time. As the Lever is Closed the cycle is repeated.
There is a few other things going on inside these Actions during Lever Operation but none of them pertain to the Feeding Process. There is the "Bolt Locking Block" which is moved up and down by the Hook on the Lever, and when fully engaged also pushes the Firing Pin Safety Pin into alignment with the Firing Pin, which pushes the end of the firing pin out far enough so that the Hammer may contact it and fire the gun.
That's pretty much it! OH,, I forgot,,, 1895's and 336's work EXACTLY the same way, and can benefit from the same tweaks.
Hope this helps.
Randy