(Another) winding question.

[second time]

Now that my GMT IIc has entered a 2 watch rotation, I am needing to wind it regularly in order to keep it going. The rotation is not particularly regular so I'm probably winding it more than absolutely necessary, but I don't want it to stop as it's set precisely and I want to avoid too much setting. If it's not being worn I generally wind it every 24 to 36 hours.

My question is this…when I start winding, the crown turns as smooth as silk. At some stage this feeling suddenly becomes a little coarser. I'm wondering if this coarseness is the mechanism to stop overwinding coming into play or just the feeling of increasing mainspring tension?