Ive been "building" since 2007 as a full time gunsmith. I've built FAL'S AR'S AK'S 1911'S bolt guns and black powder rifles. I've repaired everything from modern bullpups to antique brown Bess muskets and spent a lot of time doing trigger jobs on revolvers. I've been tinkering with rifles since highschool. I know my shit.
I know that little tid-bit about the silver solder from research with the ATF out of Denver when I put together an AR group build last year. We bought about 30 barrels from citadel and ended up with a bunch of 14"ers in leu of 16"ers. In order to keep our FFL the ATF gave us instructions on the proper way to permanently mount flash supressors.
I had my old boss read me our copy of the letter over the phonethis is what it said.
. DEPARTMENT OF THE TREASURY Bureau of Alcohol, Tobacco and Firearms Washington, D.C. 20226
JUN 18 1998
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.
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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,
The problem with silver solder comes to the melting point of the silver solder. Different brands melt at different temperatures. Actual silver soldering with flux and silver solder strip is fine, swift 50 is not. That is the gray area in which silver soldering on a part could bite you in the ass. When in doubt, go the extra step and weld. What is your freedom worth.