Silencers -or mufflers as they were often referred to at the time- seem to have been a standing item on the anti-gun agenda of the day that was tossed in the NFA with substantially no discussion.
Here is a bit of background from the National Firearms Act hearings before the Committee On Ways And Means of the House of Representatives, April 16, 1934.
Regarding revenue, since the NFA is in part a tax act.
Attorney General Cummings: I am informed that, under existing law, there is an ad valorem 10-percent tax on pistols and revolvers and that this law produced $35,388 in the fiscal year 1933. This existing law, if the pending bill should pass, will become inoperative so far as it imposes a tax on firearms included the proposed legislation. So we shall have to take into account the fact that with the passage of this bill there will disappear most if not all of that $35,000, but it will reappear in a larger measure under the taxing provisions and the licensing provisions that we would have in this act.
Mr. Cooper: I would be glad if you could give us your estimate of the revenue to be yielded from these various items suggested by you.
Attorney General Cummings: Well it probably would approach $100,000.
Mr. Cooper: All or them together would approach, in your opinion, about $100,000 a year?
Attorney General Cummings: Yes, sir.
Bearing in mind that the original NFA bill called for a tax on transfers and a license to transport across state lines, the following interchange is revealing.
Mr. McClintic: I would like to ask just one question. I am very much interested in this subject. What in your opinion would be the constitutionality of a provision added to this bill which would require registration, on the part of those who now own the type or class of weapons that are included in this bill?
Attorney General Cummings: We were afraid of that, sir.
Mr. McClintic: Afraid it would conflict with State laws?
Attorney General Cummings: I am afraid it would be unconstitutional.
Finally, a summary of the theory behind the NFA.
Attorney General Cummings: I think that it does two crucial things. It deals with the tracing of these weapons if traded or transferred after this act goes into effect; it deals with the requirement of licensing if a person is to take any weapon across State lines. And I am assuming in all this, of course, that the criminal elements are not going to obtain permits and they are not going to obtain licenses, and they are not going to be able to bring themselves within those protective requirements. Therefore, when we capture one of those people, we have simply a plain question to propound to him - where is your license; where is your permit? If he cannot show it, we have got him and his weapons and we do not have to go through an elaborate trial, with all kinds of complicated questions arising. That is the theory of the bill.