The J. Stevens Arms Co. of Chicopee Falls, Mass, introduced their Model No. 16 "Crackshot" rifle in 1900.
This was also sold with trade names such as: The Keystone, The .22 Marvel, or The .22 Spencer through various hardware & catalog stores.
That is probably what it is.
Also:
Spencer Gun Company: Trade name used by the H. & 0. Folsom Arms Company on shotguns.
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