Hello benbarclay
The earlier version of the Model 38 had a handle-mounted lever.
The feature was dropped in the late 1970s (best guess).

Here is an explanation of its use: -

Hope this helps
-------------------------------
Jack

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sb45_04_04.jpg (71.22 KB, 50 downloads)
sb_model3parts.jpg (77.43 KB, 48 downloads)