If you read the instructions on form 4473 you'll see they absolutely recognize that some receivers can only be made into long guns, yes they are still supposed to be marked other on the form. But unless you have a letter from the ATF stating specifically that their opinion says the stock can be taken off of a completed receiver and build a pistol I'm going to play it safe as their opinion is the one that matters not yours.A stock, designed to be shoulder fired, is an aspect of a rifle. But a lower with a stock is not a rifle.
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