I was curious about this, as a M16 has a barrell 16" or longer and is .22 1936 amendment removes a rifle .22 caliber or smaller, with a barrel 16" or longer, from purview of the NFA Less than 2 years after it was enacted, the Congress determined that under the NFA, "a discrimination and hardship, which was never intended, has been inflicted upon two or three manufacturers of .22 and less caliber hunting rifles." In Public Law 74-490, the Congress amended the NFA to remove a rifle of .22 caliber or smaller from purview of the NFA "if its barrel is 16 inches or more in length." The legislative history is documented in H. R. Report No. 2000, 74th Congress, 2nd Session; and in Senate Report No. 1682, 74th Congress, 2nd Session. Accordingly, the Treasury Department amended Regulations 88 in the INTERNAL REVENUE BULLETIN, Cumulative Bulletin XV-1, January-June 1936, page 468.