HIGHLY HIGHLY HIGHLY unlikely for a multitude of reasons, but as a legal matter, I point you in the direction of the Takings Clause of the 5th Amendment:
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation.
If Congress can claim a legitimate "public use" for the guns they are taking and pay us their fair value, it would theoretically be constitutional. This doctrine is known as Eminent Domain.