The second ring is where the rectum ends and the sigmoid colon begins (rectosigmoid junction). It's not a muscular sphincter like the anus, but there's a corner there that can feel tighter. It's more pronounced in some guys. If you've ever bottomed out while topping a guy you've been there. Sometimes I can work around that corner, sometimes not. Some guys have a rectum so long it can't be reached. Other guys are used to going around that corner with long dildos on their own and I get there without realizing it, but they do.
Yeah. It's an "oh fuck" or "oh my god" moment, often with a shudder for him when I get that deep. For me it's bottoming out while working a guy deep then gradually or suddenly he takes me deeper as I get round that corner maybe an inch or two into his sigmoid.
You described not only what is happening, but how amazing it feels for both the top and the bottom. There is no way either party CAN NOT feel it. It doesn't usually. just slide in. There is kind of a pop when my dick goes through.
Honestly most guys can't do it. When I press hard, it usually is painful for the bottom. I try to get them to relax and go slowly. Sometimes that does the trick but often not.
And in all fairness, not everyone's ass is the same. Guys are built differently. I was fucking this 18 year old kid for a while and from the very first fuck my dick just went through that space like butter. He felt it and loved it. So did I. You can't tell me he knew what he was doing at that age when guys that have been bottoming all their lives can't take it. This kid was born to be a bottom. He would call me up after school and ask, "Can we do it again/". How could I say no?