I sent Rainier an email, asking for some help.
A guy responded and said that they've had some real trouble getting that particular bullet to feed in Kimbers. (I sure appreciate his candor--that's refreshing!) He suggested an OAL of 1.190" and if that doesn't work to telephone him and he'd try to help me figure it out.
So, it looks like I was on the right track. I'm going to try some live rounds at 1.190" and see how it goes. Props (so far) to Rainier for their customer service!
...And I am off to shoot pins with that gun tonight at 7:00pm. I managed to squeak out a win last week. It's been a long time since anybody in the club has won two weeks in a row. I'm hoping for the best though...
