In the 1981-82 period a number of N frames are seen with both -2 and -3 features. usually it's the unpinned -3 barrel on an otherwise -2 gun, but in some cases you see the -3 cylinder. I think this is one of those.

My theory is that they started running out of the proper -2 parts and started using -3 parts to finish up the guns in production.

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