Why had Ryder forced the gem into throat in The Adventure of Blue Carbuncle?

You're likely thinking of the story "The Adventure of the Blue Carbuncle" by Sir Arthur Conan Doyle. However, in this story, Ryder never forces a gem into his throat.

Instead, the plot revolves around a valuable blue carbuncle, a diamond, which is stolen from the home of a nobleman. The thief, a young man named Ryder, ends up swallowing the gem in a moment of panic. He doesn't do so intentionally but out of fear of getting caught.

The story follows Sherlock Holmes's investigation as he tracks down Ryder, helps him retrieve the gem from his stomach, and unravels the truth behind the theft.