March 31, 1998

BATF
Firearms Technology Branch
Washington, DC 20226

Greetings:

     I had some questions about permanently attaching muzzle brakes
and barrel extensions to firearms.

     As you are aware, some barrels, particularly for some semi-
automatic rifles, come with muzzle threads. However, it may be
necessary, depending on the other features of the rifle, to remove
those threads, in order to keep the firearm from being considered
a "semi-automatic assault weapon". Additionally, some firearm
barrels come in lengths below 16 inches, and in order to be
installed on rifles without making the rifle subject to the
National Firearms Act, an extension may be permanently attached to
the end of the barrel, by muzzle threads, so as to make the barrel
length at least 16 inches.

     I was wondering what methods of attachment to muzzle threads
are considered permanent enough so as to either extend the barrel
length, by use of an extension, or to remove the muzzle threads as
a feature of a semi-automatic rifle which might otherwise be
considered a "semiautomatic assault weapon"

     In particular, I have heard that welding is acceptable. If you
can, please advise me of the method of welding, and the required
weld coverage. I have also heard that high temperature silver
solder is acceptable. If you can, please advise me as to the solder
alloy, and melting temperature that would be considered permanent.
I have also heard that some industrial adhesives are acceptable, in
particular a product called "Rocksett". I would appreciate
confirmation as to which, if any, industrial adhesives have been
found to be acceptable.

     Also, if there are any other methods which I have not
mentioned above, which have also been found to be acceptable
methods of permanently installing muzzle devices onto rifles, I
would appreciate it if you could advise me of what they are.

Sincerely,



                   DEPARTMENT OF THE TREASURY
             Bureau of Alcohol, Tobacco and Firearms
                     Washington, D.C. 20226

                           JUN 18 1998            F:FPD:FTB:RAT
                                                  3311


Dear Mr. :

This refers to your letter of March 31, 1998, in which you ask
about permanently attaching a muzzle device to various firearms.

A muzzle device, such as a muzzle brake or barrel extension, which
is attached to a barrel by means of welding or high temperature
silver solder having a melting point of at least 1,100 degrees
Fahrenheit, is considered to be part of the barrel for purposes of
measurement.  A seam weld extending at least one-half the
circumference of the barrel or four equidistant tack welds around
the circumference of the barrel are adequate for this purpose.

A firearm having a muzzle brake, cap, or barrel extension
permanently attached by those same methods to cover the threads on
a barrel, would not be considered to have a threaded muzzle. 
Please note, however, that any muzzle device or barrel extension
which functions as a flash suppressor or grenade launcher would
still constitute one of the qualifying features of a semiautomatic
assault weapon as that term is defined in 18 U.S.C. section
921(a)(30(B).  Industrial adhesive products are not an acceptable
method for permanently attaching a muzzle device.

                              - 2 -

Mr. 

We trust that the foregoing has been responsive to your inquiry. 
If you have further questions concerning this matter, please
contact us. 


                        Sincerely yours,

                            [signed]

                       Edward M. Owen, Jr.
                Chief, Firearms Technology Branch