1100*F+ Silver Solder for FH Attachment

I've got a 14.5" barrel onto which I am going to permantently mount a YHM muzzle brake QD for my YHM 762 Phantom silencer.  I've got an SBR in progress on a Form 1, but to stay legal I need this puppy on there according to BATFE specs in the meantime.

Many people blind pin and weld to accomplish this, but seeing as that's a $75 muzzle attachment I'm putting on there, I do want it to be non-destructively reversible to some degree.  That leaves me with one approved option: Silver Solder that has a melt point above 1100*F.  I have a 45% silver solder (Safety-Silv) that has a melt temp well above 1200*F, and a flow temperature above that, but I wanted to make this as easy as possible.  So, I use a soldering paste, that is a mixture of flux and finely-ground 56% silver solder in the proper ratio for use as-is.

I wanted to practice before screwing up my new Daniel Defense barrel, so I grabbed my buddy's crappy old Bushmaster and a nasty A2 flash hider, along with some peel washers.  I timed the flash hider, cleaned everything very well (including stripping the parkerizing off the threads on the OD of the barrel and ID of the flash hider), and then applied heat fence (a heat sink material) to the bore and outside of the barrel.  I put an even layer of the solder paste on the barrel threads, slid the peel washers in place, and snugged up the A2.

I placed the barrel inside the pipe-holding side of my bench vise (lined with cardboard to make sure the finish didn't get screwed up), so I could turn it as I heated it, and applied heat with a MAPP gas torch.  It took about 2-3 minutes of constant heating and rotation to get the flash hider, peel washers, and very tip of the exposed barrel cherry red (around 1300-1400*F), as which point I could clearly see the solder flowing as I rotated it.  I kept heating it with rotation for another 20-30 seconds, and then let it cool down.

I tried to remove it after cooling, but the bench top into which the viser is mounted was flexing, with absolutely no movement of the flash hider.  Success!

I think it is an attractive brazed joint, and it will meet all legal requirements when performed on my 14.5" barrel and silencer QD mount to make that barrel 16"+ long.  I might try to hit this with some cold bluing agent to see what that does, but honestly I paint my carbines (like EVERYONE should) so it won't be visible after I hit it with the Aervoe anyways.

Okay, here are the results on my DD 14.5" CHF LW barrel, with YHM 5.56 Muzzle Brake QD mount, Aero Precision upper with BCM parts, and Midwest Industries 12" Gen1 rail:

No issues at all except for my dumb ass clocking the brake 180* out of phase and then having to set everything up again to reheat and reclock.  The LW profile does look a little funny supporting the QD mount, but I'll get over it.  I'm taking out my new chronograph tomorrow for first testing.  No M193 to speak of, so it's handloads for now.