I have MM manual S-148, "Assembly, Operation, and maintenance Manual Model E Corn Sheller". Page 16 and 17 describe the spring loaded damper and adjustable shutter at the output of the cylinder. Instructions say to adjust damper spring and shutter opening to remove all kernels from the cob, but not to chop the cobs into small pieces and get cob particles in the shelled corn.
I assume this is the automatic gate you mentioned. I've never seen an Ottawa sheller so don't know about it.
My dad wore out 3 Model E shellers and don't remember him ever doing much adjusting once he got it set.