Looks like a nice late-style Field Grade.
The basic "box" of the standard NID frame is the same size from the .410-bore through the Super-Ten. The height and width of the standing breech and the firing pin spacing increases along with the bore size. From the guns I've measured the firing pin spacing on the .410-bore and 28-gauge guns is 15/16 inch. For the 20-gauge 1 inch. For the 16- and 12-gauges 1 1/8 inch and for the Super-Ten 1 1/4 inch.
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