I found a couple over the years in batches of GI Buttplates. They are not commercial. My guess is either a production error, or a very late small contract. The reason I say the second option is possible is because there was a very small M14contract for Garand buttplates which had inward dimples. It was a short production during the early days of the M14, to supplement the shortage of flapper type buttplates during rifle production. The buttplate used a hard rubber type spacer.
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