Rear sight is "H" in shield. "H" also on left lug of bolt. Gunboards is saying L.R.Co. 7160060 ones were the most common, but a limited number of "H" ones were used. We have a small "G" under the "H" on the bolt. New pics added to the first.

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1944 IBM M1 Carbine Slideshow by majspud | Photobucket