Watched "Sierra" last night. Another of those films where Audie was said to be "wooden" and I can see that in some scenes where his character is supposed to be secretive and holding back from interacting with people but there were some terrific moments where his face showed flickers of emotion that were just perfect for the story line.
Murphy takes a lot of flak for his "early" performances but frankly I think what he does in these movies compares very favorably to what Wanda Hendrix (Sierra) or Brian Donlevy (Kansas Raiders) are doing opposite. I can enjoy over the top and silly, but Wanda and Donlevy are just annoying in those films imo.
As far as the chemistry between the leads in Sierra, it seemed to me kind of one-sided, like she was still pretty into him but he was largely over her. Just my opinion.
I don't remember any particular stories about Murph falling off a horse on this production, but I believe he was still learning to ride at the time, so it's possible.
There is some confusion about whether the incident with Tony Curtis happened on this shoot or on Kansas Raiders. Something very similar to it is mentioned in the press materials for Sierra, without naming the actor on the receiving end of Murph's prank, but Tony Curtis and James Best both claim that Murph pranked Curtis using a gun loaded with blanks during the Kansas Raiders shoot.
Curtis claimed that he and Murph became pretty good friends after the incident, fwiw. I always thought the line about "I don't think I'm the type, maybe Tony Curtis would do," was more a joke and a potshot at the studio heads and their priorities than a serious suggestion. But again, just my opinion.